LI  BRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 

GIFT    OF 


-SO 


Received 
^  ccessions  No.  £3&4/!'     Shelf  No. 


AMERICAN  WEATHER 


A   POPULAR   EXPOSITION    OF 


THE   PHENOMENA  OF  THE  WEATHER, 


INCLUDING  CHAPTERS   ON 


HOT  AND  COLD  WAVES,  BLIZZARDS,    HAIL- 
STORMS AND  TORNADOES, 


ETC.,   ETC. 


ILLUSTRATED  WITH  52  ENGRAVINGS  AND  TWENTY- FOUR  CHARTS. 


BY  GEN.   A.  W.   GREELY, 

Chief  Signal  Officer,  United  States  Army. 


TJSIVBE3IT7 


NEW   YORK: 
DODD,    MEAD    &    COMPANY, 

PUBLISHERS. 


COPYRIGHT,  1888, 
Br  DODD,  MEAD  &  COMPANY. 


PEEFAOE. 


THE  object  of  this  work  is  to  give  clearly  and  simply, 
without  the  use  of  mathematics,  an  idea  of  meteorology 
in  general,  supplemented  by  climatic  data  regarding 
temperature,  rainfall,  wind,  and  storms,  especially  of 
our  own  country. 

The  examples  cited  in  most  modern  works  are,  in 
great  part,  drawn  from  foreign  sources,  so  that  the 
author  has  felt  the  advisability  of  setting  before  the 
American  public  in  some  detail  the  fact  that  there  can 
be  found  in  the  United  States  all  varieties  of  weather. 
The  delightful  climate  of  the  Riviera,  the  burning 
heats  of  the  Sahara,  and  the  eternal  frosts  of  Siberia 
find  their  parallels  within  the  broad  confines  of  our 
Union. 

The  violence  of  our  tornadoes  and  hurricanes,  the 
extremes  of  heat  and  cold,  the  absence  of  rain  or  its 
enormous  superabundance,  the  number  of  storms,  and 
the  size  of  hail  stones,  together  with  the  prolonged 
heated  terms  of  summer  and  the  phenomenal  and  ex- 
tensive cold  waves  of  winter,  prove  that  one  need  not 
quit  America  to  experience  the  most  wondrous  action 
of  nature's  forces. 

Ferrel' s  elaborate  and  mathematical  treatise  on  mete- 
orology covers  very  fully  the  scientific  field  at  the  pres- 
ent time,  but  the  author  knows  of  no  plain  and  simple 
American  book,  other  than  that  of  Loomis,  which  that 
distinguished  meteorologist  has  not  rewritten  in  the 
light  of  our  present  knowledge. 


IV  PREFACE. 

The  author  acknowledges  his  indebtedness  to  the 
valuable  memoirs  and  publications  of  Abercrombie, 
Blanford,  Buchan,  Loomis,  and  Scott.  He  has  also 
utilized  the  official  writings  and  publications  put  forth 
by  the  Army  Signal  Office.  No  great  claim  for  orig- 
inality is  set  forth,  although  the  author  has  supple- 
mented and  modified  the  statements  and  opinions  of 
other  meteorologists  and  occasionally  advanced  new 
ideas,  the  result  of  his  many  years  of  study  and  prac- 
tice in  meteorological  work,  and  of  his  personal  labors 
as  a  predicting  officer. 

The  thanks  of  the  author  are  due  for  timely  sugges- 
tions to  Professor  Thomas  Russell,  who  has  rendered 
valuable  aid  in  correcting  the  proof-sheets. 

A.  W.  GREELY. 

WASHINGTON,  October  1,  1888. 


TABLE  OF  CONTENTS. 


CHAPTER  I. 
INTRODUCTORY 1 

CHAPTER  II. 
THE  ATMOSPHERIC  PRESSURE,  AND  HOW  MEASURED      .        .        .5 

CHAPTER  III. 
TEMPERATURE  .        .        . .18 

CHAPTER  IV. 
RADIATION         .        .        .        .        .        .        .      • .      T~~     .        .35 

CHAPTER  V. 
HUMIDITY  AND  EVAPORATION 45 

CHAPTER  VI. 
WINDS 53 

CHAPTER  VII. 
PRECIPITATION — FOG,  CLOUD,  RAIN,  AND  SNOW  .        .        .        .60 

CHAPTER  VIII. 
THE  DISTRIBUTION  OF  ATMOSPHERIC  PRESSURE  .        .        .        .82 

CHAPTER  IX. 
THE  DISTRIBUTION  OF  TEMPERATURE 100 

CHAPTER  X. 
THE  RANGE,  VARiAjBH£X!E£24se^ExTREMEs  OF  TEMPERATURE  .  120 


v  TABLE   OF   CONTENTS. 

CHAPTER  XL  PAGE 

DISTRIBUTION  OF  RAIN  AND  SNOW         .        .        .  .        .134 

CHAPTER  XII. 
THE  WINDS  OF  THE  UNITED  STATES     .        .        .        .        .        .  163 

CHAPTER  XIII. 
Low- AREA  STORMS   .        .    '*..   •    f       v       .        .       .        .        .178 

CHAPTER  XIV. 
CYCLONES  AND  HURRICANES    ...        .        .        »        .        .  193 

CHAPTER  XV. 
HIGH- AREA  STORMS         .        *       ,        .        .        .        »   .    .     ".  202 

CHAPTER  XVI. 
COLD  WAVES  AND  BLIZZARDS          .        .        .        .        v       .        .  211 

CHAPTER  XVII. 
TORNADOES      .         . 228 

CHAPTER  XVIII. 
HAIL,  THUNDER,  AND  DUST  STORMS 235 

CHAPTER  XIX. 
DROUGHTS  AND  HEATED  TERMS     .        .       .        ....  246 

CHAPTER  XX. 
MISCELLANEOUS  PHENOMENA  .        .        .        .      ...       ,       .        .  255 

CHAPTER  XXI. 

WEATHER  PREDICTIONS   .  *  *.  .  .  264 


LIST  OF  TABLES. 


PAGE 

TABLE    1.  CORRECTIONS  FOR  TEMPERATURE  OF  BAKOMETEK  TO  32°  273 

"  2.  CORRECTIONS  FOR  ELEVATION  OF  BAROMETER  ; — TO 

1500  FEET 274 

"  3.  APPROXIMATE  CORRECTIONS  TO  REDUCE  HOURLY 

BAROMETRIC  READINGS  TO  MEAN 275 

"  4.  APPROXIMATE  CORRECTIONS  TO  DEDUCE  MEAN  TEM- 
PERATURE FROM  MAXIMUM  AND  MINIMUM 275 

"  5.  DEW-POINTS  WITH  EQUIVALENT  VALUES  OF  VAPOR 
TENSION,  AND  GRAIN  OF  WATER  TO  EACH  CUBIC 
FOOT  OF  AIR 276 

"  6.  VARIATIONS  OF  MAGNETIC  NEEDLE  IN  THE  UNITED 

STATES 276 

"  7.  RECORD  OF  HIGHEST  AND  LOWEST  TEMPERATURES  IN 

EACH  STATE 278 

"  8.  RECORD  OF  GREATEST  MONTHLY  RAINFALL  IN  EACH 

STATE 277 

"  9.  AVERAGE  DATES  OF  FIRST  KILLING  FROST  AT  SELECT- 
ED STATIONS  EN  THE  UNITED  STATES 280 


LIST  OF  OHAETS. 


PAGE 

No.        I.  ANNUAL  MEAN  PRESSURE  OF  THE  NORTHERN  HEMI- 
SPHERE      83 

"  II.  PRESSURE,  BY  DEPARTURES,  OVER  THE  UNITED  STATES, 
WITH  PREVAILING  WINDS,  FOR  THE  MONTH  OF  JANU- 
ARY   91 

"       III.  PRESSURE,  BY  DEPARTURES,  OVER  THE  UNITED  STATES, 

WITH  PREVAILING  WINDS,  FOR  THE  MONTH  OF  APRIL.  93 
"  IV.  ANNUAL  MEAN  TEMPERATURE  OF  THE  NORTHERN 

HEMISPHERE 101 

"  V.  MEAN  TEMPERATURE  OF  THE  UNITED  STATES  FOR  THE 

COLDEST  MONTH  (JANUARY) 109 

"  VI.  MEAN  TEMPERATURE  OF  THE  UNITED  STATES  FOR  THE 

WARMEST  MONTH  (JULY) Ill 

"  VII.  ABSOLUTE  MAXIMA  TEMPERATURE  OF  THE  UNITED 

STATES 121 

"    VIII.  ABSOLUTE   MINIMA   TEMPERATURE   OF  THE  UNITED 

STATES 129 

"       IX.  SHOWING  CONTINUANCE  IN  Tine  UNITED  STATES  OF 

MEAN  DAILY  TEMPERATURES  ABOVE  50° 113 

X.  SHOWING  CONTINUANCE  IN  THE  UNITED  STATES  OF 

MEAN  DAILY  TEMPERATURES  BELOW  32° 115 

"       XI.  VARIABILITY  OF  TEMPERATURE  IN  THE  UNITED  STATES 

FOR  JANUARY 133 

"  XII.  ANNUAL  MEAN  RAINFALL  OF  THE  NORTHERN  HEMI- 
SPHERE   135 

"    XIII.  MEAN  RAINFALL  IN  THE  UNITED  STATES  FOR  APRIL.  139 


X  LIST   OF   CHARTS. 

PAGE 

No.  XIV.  MEAN  RAINFALL  IN  THE  UNITED  STATES  FOR  MAY...  143 
"  XV.  MEAN  RAINFALL  IN  THE  UNITED  STATES  FOR  JUNE..  145 
"  XVI.  AVERAGE  MEAN  CLOUDINESS  IN  THE  UNITED  STATES 

FOR  JANUARY 67 

"  XVII.  AVERAGE  MEAN  CLOUDINESS  IN  THE  UNITED  STATES 

FOR  AUGUST 65 

"  XVIII.  MEAN  ABSOLUTE  HUMIDITY  OF  THE  UNITED  STATES 

(IN  GRAINS  OF  AQUEOUS  VAPOR  TO  A  cu.   FT.  OF 

AIR)  FOR  JANUARY 49 

"  XIX.  MEAN  ABSOLUTE  HUMIDITY  OF  THE  UNITED  STATES 

(IN  GRAINS  OF  AQUEOUS  VAPOR  TO  A  cu.  FT.   OF 

AIR)  FOR  JULY 53 

"  XX.  MEAN  TRACK  OF  Low- AREA  STORMS  OVER  THE 

NORTHERN  HEMISPHERE  IN  DECEMBER 181 

"  XXI.  MEAN  TRACK  OF  Low- AREA  STORMS  DURING  AUGUST 

OVER  THE  NORTHERN  HEMISPHERE 183 

"  XXII.  AVERAGE  DATES  OF  FIRST  KILLING  FROSTS  IN  THE 

UNITED  STATES Frontispiece. 

"  XXIII.  AVERAGE  DATES  OF  LAST  KILLING  FROSTS  IN  THE 

UNITED  STATES 269 

"  XXIV.  GEOGRAPHICAL  DISTRIBUTION  IN  THE  UNITED  STATES 

OF  ALL  RECORDED  TORNADOES.  .  .  229 


LIST  OF  ENGEAYINGS. 


PAGE 

FIGURE  No.  1,  STANDARD  BAROMETER 7 

"        "     2.  ECCARD'S  RECORDING  BAROMETER 14 

"        "3.  RICHARD'S  REGISTERING  BAROMETER 16 

"        "     4.  RICHARD'S  REGISTERING  THERMOMETER 27 

"        "     5.  DRAPER'S  REGISTERING  THERMOMETER.  . , 28 

"        "     6.  DRY  AND  WET  THERMOMETERS,  MOUNTED 30 

"        "     7.  MAXIMUM       AND      MINIMUM      THERMOMETER, 

MOUNTED , 32 

"        "     8.  PICHE'S  EVAPOROMETER 47 

"        "     9.  KOPPE'S  HAIR  HYGROMETER 49 

"        "    10.  REGNAULT'S  HYGROMETER 50 

"        "    11.  SELF-REGISTER    FOR    RAIN,    DIRECTION    AND 

VELOCITY  OF  THE  WIND 55 

"        "    12.  ROBINSON'S  ANEMOMETER 57 

"        "    13.  MONTHLY  FLUCTUATIONS  OF  CLOUDINESS 67 

"        "    14.  UNITED   STATES   SIGNAL    SERVICE   RECORDING 

RAIN-GAUGE 75 

"        "    15.  ECCARD'S  RECORDING  RAIN-GAUGE 76 

"   16.  TYPICAL  FORMS  OF  HAIL 79 

"       *'    17.  TYPICAL   MONTHLY  FLUCTUATIONS  OF   ATMOS- 
PHERIC PRESSURE 88 

"        "    18.  HOURLY  BAROMETRIC  OSCILLATIONS 95 

"        "19.  MONTHLY  FLUCTUATIONS  OF  TEMPERATURE 107 

"        "    20.  HOURLY  MARCH  OF  TEMPERATURE  .                  .  113 


xii  LIST  OF  ENGRAVINGS. 


PAGE 


FIGURE  No.  21.  INTERRUPTIONS  OF  TEMPERATURE  (COLD  DAYS 

OF  MAY) 117 

"        "22.  MONTHLY  FLUCTUATIONS  OF  DAILY  RANGE  OF 

TEMPERATURE 125 

"        "    23.  MONTHLY  FLUCTUATIONS  OF  RAINFALL 141 

"        "24.  MONTHLY  PROBABILITIES  OF  RAINY  DAYS 151 

"        "25.  HOURLY  VARIATIONS  OF  RAIN  AT  NEW  YORK 

CITY 156 

"        "26.  WINDROSE    OF    AVERAGE   WIND    TRAVEL    AT 

WASHINGTON,  1884-87 168 

"        "27.  MONTHLY  FLUCTUATIONS  OF  WIND  VELOCITY.  .  171 
"        "28.  HOURLY  FLUCTUATIONS  OF  WIND  VELOCITY  IN 

MARCH 174 

"        "29.  COMPARATIVE  VELOCITIES  OF  UPPER  AIR  CUR- 
RENTS AND  STORM  CENTRES 187 

"    30.  CYCLONE  OF  AUGUST  16TH-22D,  1888 194 

"        "31.  ANTI-CYCLONE  JANUARY  6ra-12TH,  1886 207 

"        "32.  LUNAR   HALO   AT   FORT    CONGER,   FEBRUARY, 

1882..  .  260 


AMERICAN  WEATHER. 


CHAPTER  I. 

INTRODUCTORY. 

FROM  the  beginning  of  time  the  alternation  of  the 
seasons  and  the  irregular  recurrence  of  weather  condi- 
tions must  have  interested  man  and  engaged  his  atten- 
tion. The  very  ancient  Book  of  Job  and  the  later  books 
of  the  New  Testament  contain  formulated  weather 
wisdom,  the  result  of  man's  primitive  observations. 
The  ancient  classical  writers  dwelt  much  on  weather 
phenomena,  but  owing  to  ignorance  of  physical  laws, 
made  no  substantial  advances  in  formulating  them. 

The  invention  of  the  air-thermometer  near  the  end 
of  the  sixteenth  century  (by  some  attributed  to  Sanc- 
torio,  of  Padua,  1590),  and  of  the  barometer,  by  Torri- 
celli,  in  1643,  afforded  the  first  reliable  means  of  instru- 
mental observations  of  the  temperature  and  pressure 
of  the  air.  It  is  only  within  the  last  hundred  years 
that  the  acute  and  remarkable  meteorological  essays 
of  Dalton  awakened  the  attention  of  scientific  men  to 
the  fact  that  the  principles  of  philosophy  were  suffi- 
cient to  explain  the  intricate  and  varied  phenomena  of 
the  atmosphere.  Since  the  beginning  of  the  century 
very  much  has  been  done  to  lay  the  solid  foundations 
of  meteorology  as  an  exact  science  by  amassing  data, 


2  AMERICAN  WEATHER. 

formulating  conditions,  disproving  unsound  theories, 
and  in  evolving  a  few  general  laws. 

The  theory  of  dew,  the  exact  relation  of  winds  to 
varying  atmospheric  pressures,  the  deflecting  influence 
exerted  by  the  rotary  motion  of  the  earth,  and  the 
gyratory  system  of  storm  winds  are  doubtless  the  most 
important  subjects,  whose  elucidation  has  enriched 
theoretical  meteorology  during  this  time. 

The  term  meteorology  originally  included  astronom- 
ical phenomena,  but  by  common  consent  it  now  relates 
only  to  weather  and  climate.  In  this  work  the  writer 
intends  to  discuss  more  particularly  the  climatic  con- 
ditions of  the  United  States,  treating  of  the  weather 
conditions  only  so  far  as  may  be  needful  to  set  forth 
the  subject  simply  and  generally. 

The  average  composition  of  dry  atmospheric  air, 
according  to  Ferrel,  consists  of  oxygen  by  volume 
20.95,  and  by  weight  23.16  per  centum  ;  nitrogen,  79.02 
volume,  76.77  weight ;  carbonic  acid,  0.03  volume, 
0.046  weight.  In  addition  to  these  main  constituents, 
measurable  quantities  of  ammonia,  ozone,  and  traces 
of  carburet  ted  and  sulphuretted  hydrogen,  nitric  and 
sulphurous  acids  also  exist.  The  atmosphere,  how- 
ever, is  never  entirely  dry,  but  contains  water  in  the 
shape  of  aqueous  vapor,  which  is  irregularly  distrib- 
uted in  largely  varying  quantities. 

The  actual  height  of  the  atmosphere  is  assumed  to 
be  about  two  hundred  miles  above  the  surface  of  the 
earth,  but  the  rarefaction  of  the  air  increases  so  rapidly 
with  elevation  that  seven  or  eight  miles  is  about  the 
limit  at  which  mammals  or  birds  can  live.  Sir  James 
Glashier,  September  5th,  1862,  ascended  in  a  balloon 
from  Wolverhampton,  England,  to  about  the  height  of 
seven  miles,  and  barely  escaped  death. 

Although  it  is  uncertain  whether  the  constituents  of 


AMERICAN  WEATHER.  3 

the  atmosphere  are  equally  distributed,  yet,  as  obser- 
vation shows  no  material  difference  at  great  elevations, 
it  has  been  assumed  that  continually  ascending  and 
descending  air  currents  cause  the  proportion  of  gases 
to  be  substantially  constant  throughout  the  different 
air  strata. 

The  determination  of  the  exact  physical  conditions 
of  the  atmosphere  involves  the  ascertaining  by  instru- 
ments of  its  temperature,  its  pressure,  the  amount  of 
evaporation  or  condensation  of  aqueous  vapor — whether 
invisible  or  in  the  form  of  clouds,  rain,  etc. — and  the 
amount  of  transference  from  one  point  of  the  earth's 
surface  to  another,  as  indicated  by  prevailing  winds  or 
the  silent,  but  no  less  important,  movement  of  the 
mercurial  column.  In  addition  may  also  be  noted  the 
quantity  and  kind  of  atmospheric  electricity,  the 
amount  of  ozone,  the  manifestations  of  the  aurora,  and 
the  presence  or  absence  of  meteors  and  various  optical 
phenomena,  such  as  halos,  coronas,  etc.  The  mani- 
festations of  terrestrial  magnetism,  formerly  conjoined 
with  meteorology,  should  no  longer  be  considered  ex- 
cept as  a  separate  branch  of  the  physical  sciences. 

The  abiding  interest  in  meteorology  displayed  by  the 
people  of  the  United  States  results  from  the  more  or 
less  successful  efforts  to  determine  from  instrumental 
readings  and  observations  the  special  conditions  that 
indicate  the  development,  advance,  and  progress  of  the 
atmospheric  disturbances,  which,  resulting  in  storms 
of  greater  or  less  violence,  cause  enormous  destruction 
of  property  and  often  considerable  loss  of  life. 

Theoretical  meteorology  involves  a  careful  consider- 
ation of  all  phases  of  such  disturbances,  even  the  most 
minute,  since  any  theory  of  weather  predictions  based 
on  other  than  sound  reasonings  and  an  accurate  study 
of  physics  must  be  considered  one  of  the  worst  forms 


4  AMERICAN  WEATHER. 

of  empiricism.  The  spirit  of  the  day  especially  de- 
mands, however,  that  scientific  research  shall  show  the 
widest  range  of  practical  results,  and  so  all  systems  of 
weather  predictions  and  storm  warnings  should  be 
supplemented  by  the  taking  and  collating  of  such  ob- 
servations as  may  lead  to  a  thorough  knowledge  of 
that  local  sanitary  meteorology  so  important  to  the 
welfare  of  great  cities,  and  as  to  the  fitness  of  local 
climates  as  a  means  either  of  extending  the  scope  and 
extent  of  national  industries  or  of  alleviating  human 
suffering  and  saving  human  life. 


CHAPTER  II. 

THE    ATMOSPHEEIC    PRESSURE,    AND    HOW    MEASURED. 

THE  pressure  of  the  atmosphere  on  the  earth  is 
measured  by  a  barometer,  either  mercurial  or  aneroid, 
the  readings  of  which  give  the  air  pressure  expressed 
in  inches  of  pure  mercury.  For  instance,  the  reading 
29.92  indicates  that  the  weight  of  the  air  (with  its 
aqueous  vapor,  etc.)  over  that  part  of  the  earth  is  equal 
to  the  weight  of  a  layer  of  mercury  of  the  depth  of 
twenty -nine  and  ninety-two  hundredths  inches. 

The  pressure  of  an  atmosphere,  considered  as  a 
unit,  is  the  weight  of  a  column  of  pure  mercury  at  a 
temperature  of  32°  *  at  the  height  of  29.92  inches  (760 
mm.),  in  latitude  45°,  at  the  level  of  the  sea. 

The  pressure  of  the  air  in  the  United  States  at  the 
level  of  the  sea  is  about  14.7  pounds  on  each  square 
inch  of  surface.  As  the  elevation  of  the  land  above 
the  mean  sea-level  increases,  the  pressure  of  the  air 
decreases  ;  and  since  the  specific  gravity  of  mercury  is 
13.60,  the  pressure  of  the  air  at  any  elevation  can  easily 
be  determined  from  the  height  at  which  the  mercury 
stands  in  the  barometer. 

The  principle  of  the  barometer  is  the  well-known  and 
simple  one  on  which  depends  the  action  of  the  common 
pump — viz.,  that  a  tube  filled  and  sealed  at  one  end 
and  inverted  into  liquid  such  as  the  tube  contains 


*  All  temperatures  in  this  work  are  in  degrees  Fahrenheit,  except 
when  marked  C.  (Centigrade). 


6  AMERICAN   WEATHER. 

empties  only  partly,  owing  to  atmospheric  pressure 
being  exerted  only  on  the  exterior  surface. 

A  glass  tube  of  uniform  bore,  three  feet  long  and  half 
an  inch  in  diameter,  filled  with  pure  mercury,  best 
answers  for  the  purpose  of  measuring  the  atmospheric 
pressure.  The  tube  before  being  filled  must  be  care- 
fully dried,  since  any  moisture  remaining  in  the  vacu- 
um at  the  top  of  the  tube  would  be  converted  into 
aqueous  vapor,  which,  when  present,  presses  downward 
on  the  top  of  the  column  with  a  force  varying  with  the 
temperature,  and  causes  the  mercury  to  sink  too  low. 
The  mercury  moving  freely  in  the  tube  is  in  equilibri- 
um with  the  weight  of  the  atmosphere,  and  its  surface 
ascends  or  descends  as  the  pressure  increases  or  de- 
creases. Near  the  level  of  the  sea  pure  mercury 
usually  descends  until  its  height  is  about  thirty  inches 
above  the  surface  of  the  mercury  in  which  the  tube  is 
plunged. 

The  barometer  in  general  use  is  a  straight  glass  tube 
securely  fixed,  with  a  scale  permanently  attached 
thereto.  Fortin's  device,  which  is  now  applied  to  all 
standard  barometers,  consists  in  raising  or  lowering 
the  mercury  in  the  cistern,  by  a  screw,  until  its  surface 
is  brought  to  the  level  of  an  ivory  point,  which  serves 
as  the  zero  of  the  scale.  It  is  not  convenient  to  have  a 
scale  extending  the  whole  length  of  the  barometer. 
Usually  a  short  scale,  covering  the  range  of  extreme 
fluctuation,  is  securely  fastened  to  the  metal  casing 
which  surrounds  the  glass  tube. 

This  casing  in  an  improved  standard  barometer  (see 
Fig.  1)  consists  of  a  brass  tube  terminating  at  top  in 
a  ring  for  suspension,  and  at  bottom  in  a  flange  to 
which  the  cistern  is  attached.  The  upper  part  of  this 
tube  is  cut  through  so  as  to  expose  the  glass  tube  and 
mercurial  column  within.  Attached  at  one  side  of 


AMEKICAN  WEATHEK. 


this  opening  is  a  scale,  graduated  in 
inches  and  parts,  and  inside  this  slides 
a  short  tube,  connected  to  a  rack- work 
arrangement,  moved  by  a  milled  head  ; 
this  sliding  tube  carries  a  vernier  in 
contact  with  the  scale,  which  reads  to 
.010,  and  in  some  cases  to  .002  inch. 

In  the  middle  of  the  brass  tube .  is 
fixed  a  thermometer,  the  bulb  of  which, 
externally  covered  but  inwardly  open 
and  nearly  in  contact  with  the  glass 
tube,  indicates  the  temperature  of  the 
mercury  in  the  barometer  tube.  This 
central  position  of  the  thermometer  is 
selected  that  the  mean  temperature  of 
the  whole  column  may  be  obtained — a 
matter  of  importance. 

The  cistern  is  made  up  of  a  glass  cyl- 
inder, which  allows  the  surface  of  the 
mercury  to  be  seen,  and  a  top  plate, 
through  the  neck  of  which  the  barom- 
eter tube  passes  and  to  which  it  is  fast- 
ened by  a  piece  of  kid  leather,  making 
a  strong,  flexible  joint.  To  this  plate, 
also,  is  attached  a  small  ivory  point, 
the  extremity  of  which  marks  the  bot- 
tom or  zero  of  the  scale  above.  The 
scale  is  laid  off  in  England  and  America 
in  English  inches — the  height  of  which 
is  very  carefully  determined  with  ref- 
erence to  the  zero  point.  The  scale 
covers  a  range  of  four  inches  or  more, 
usually  from  twenty-seven  to  thirty- 
one  inches  when  to  be  used  near  the 
level  of  the  sea.  ^  Jk^eree^serves  to  ad- 
just the  mercury  to  the  ivory  point,  and 


FIG.  l. 
Standard  Barometer. 


8  AMERICAN  WEATHER. 

also  by  raising  the  leather  bag,  which  forms  the  lower 
part  of  the  cistern,  contracts  and  completely  fills  the 
tube  and  it  with  mercury,  and  puts  the  instrument 
in  condition  for  transportation. 

The  tube  is  sometimes  bent  in  the  form  of  a  siphon, 
in  which  case  the  height  of  the  mercurial  column  is 
measured  with  reference  to  the  surface  of  the  mercury, 
at  the  open  end.  Siphon  barometers  are  frequently 
used  for  automatic  registration,  and  in  such  instru- 
ments the  zero  of  the  scale  is  movable. 

The  fixed  scale  is  usually  divided  to  tenths  of  inch- 
es, but  to  insure  greater  accuracy,  a  movable  scale, 
called  a  vernier,  is  arranged  so  it  can  be  moved  up  and 
down  the  fixed  scale  with  ease  and  precision.  The 
vernier  has  ten  principal  divisions,  which  are  exactly 
the  same  length  as  nine  divisions  of  the  fixed  scale,  so 
that  each  vernier  division  is  just  one  tenth  less  than  a 
scale  division,  or  equivalent  to  0.010  inch.  The  ob- 
server reads  on  the  fixed  scale  the  inches  and  tenths  of 
inches  next  'below  the  lower  edge  of  the  vernier,  and 
from  the  vernier  itself  reads  off  the  hundredths  of 
inches,  which  are  found  by  noting  the  vernier  line 
which  exactly  or  most  nearly  coincides  with  a  scale 
division.  If  the  marks  coincide  the  reading  is  even 
hundredths,  and  a  zero  can  be  put  in  the  place  of 
thousandths  ;  but  if,  as  generally  happens,  no  vernier 
mark  coincides  exactly,  the  thousandths  of  an  inch 
can  be  estimated. 

Some  barometers  have — a  preferable  arrangement— 
the  fixed  scale  divided  to  twentieths  of  an  inch,  in 
which  case  the  vernier  has  twenty-one  divisions,  equal 
to  twenty  on  the  scale,  and  the  reading  is  made  directly 
to  the  nearest  thousandth  of  an  inch. 

While  persons  of  ordinary  intelligence  can  in  a  few 
minutes  learn  how  to  read  a  barometer  accurately,  yet 


AMERICAN  WEATHER.  9 

to  insure  satisfactory  observations  the  observer  must 
not  only  be  careful  and  methodical,  but  also  should 
understand  the  various  sources  of  error  and  the  means 
of  correcting  them. 

The  instrument  should  be  vertical  and  the  tempera- 
ture—to be  kept  as  equable  as  possible — first  be  deter- 
mined ;  the  cistern  mercury  under  a  good  light  and 
exactly  level  with  the  zero  point ;  the  vernier  set  so 
that  its  front  and  back  edges  are  just  tangent  to  the 
meniscus,  or  rounded  top  of  the  mercury  surface, 
while  the  eye  should  be  at  the  same  height.  Headings 
both  of  the  attached  thermometer  and  vernier  should 
be  verified  after  being  recorded,  and  to  insure  greater 
accuracy  it  is  advisable  to  mentally  calculate  the 
change  since  the  last  reading,  and  if  unusual,  to  make 
a  second  reading. 

It  is  well  to  correct  two  popular  but  erroneous  ideas 
regarding  the  location  and  the  observed  reading  of  the 
barometer.  It  is  not  necessary  that  the  instrument 
should  be  situated  out  of  doors,  since  the  atmospheric 
pressure  is  the  same  in  the  house.  Again,  the  words 
"fair,"  "change,"  "stormy,"  which  appear  on  the 
scale  of  many  barometers,  have  no  special  signifi- 
cance, except  for  some  particular  locality,  and,  indeed, 
are  often  misleading.  The  continuance  of  fair  or 
stormy  weather,  or  the  change  from  one  to  the  other, 
is  betokened  by  the  fluctuations  and  not  by  the  mere 
height  at  which  the  mercury  stands. 


Corrections  must  be  applied  to  all  barometer  read- 
ings in  order  that  those  of  different  instruments  may 
be  strictly  comparable  with  each  other,  and  so  be 
readily  used  for  scientific  purposes.  Some  corrections 


10  AMERICAN  WEATHER. 

have  reference  to  the  special  instrument,  while  others 
are  of  general  application. 

The  correction  for  instrumental  error  is  applied  to 
reduce  the  readings  of  an  individual  instrument  to  any 
particular  standard.  It  is  additive  (+)  if  the  barom- 
eter reads  too  low,  or  subtractive  (— )  if  it  reads  too 
high. 

CORRECTION  FOR  CAPILLARY  ACTION. 

The  correction  for  capillarity  is  always  additive, 
since  barometers  are  affected  by  the  capillary  action 
between  the  glass  tube  and  the  mercury,  the  effect  of 
which  is  constantly  to  depress  the  mercury  by  a  cer- 
tain quantity  nearly  inversely  proportional  to  the 
diameter  of  the  tube. 

This  depression  is  greater  in  tubes  in  which  the  mer- 
cury has  not  been  boiled  than  in  those  which  have 
been  subjected  to  this  process.  The  amount  of  this 
depression  in  boiled  tubes,  according  to  Buchan,  is  as 
follows :  If  the  diameter  of  the  tube  is  0.1  inch,  the 
depression  of  mercury  is  0.070  ;  if  0.2  inch,  0.029  ;  if 
0.3  inch,  0.014  ;  if  0.5,  0.003  inch.  Most  makers  allow 
for  this  by  depressing  the  scale  in  each  barometer  just 
sufficient  to  offset  the  capillary  action. 

Certificates  furnished  generally  include  the  correc- 
tions above  mentioned,  as  far  as  any  of  them  are  appli- 
cable to  that  special  barometer. 

CORRECTION  FOR  TEMPERATURE. 

In  consequence  of  the  great  risk  of  the  heat  of  the 
observer's  person  affecting  the  thermometer  attached 
to  the  instrument  during  the  process  of  taking  a  read- 
ing of  the  barometer,  the  attached  thermometer,  as  has 
been  said,  should  always  be  recorded  before  the  read- 
ing of  the  barometrical  column  is  made.  As  is  well 


AMERICAN   WEATHER.  11 

known,  all  bodies  are  affected  in  their  dimensions  by 
heat,  and  in  taking  accurate  measure  of  any  object,  it 
is  necessary  to  know  at  what  temperature  the  measure 
was  made,  in  order  to  determine  what  the  length  would 
have  been  at  some  definite  standard  temperature. 

The  very  considerable  changes  in  the  volume  of  mer- 
cury, caused  by  varying  temperatures,  renders  it  neces- 
sary for  purposes  of  comparison  that  the  height  of  a 
column  should  be  reduced  to  a  standard  temperature. 
By  common  consent  of  physicists  this  standard  is  32° 
(0  C.) — the  temperature  of  melting  ice.  The  amount 
of  this  correction  is  about  0.0027  inch  for  each  degree 
Fahrenheit.  For  convenience,  tables  have  been  calcu- 
lated from  which  the  proper  corrections  can  be  obtained 
by  inspection.  (See  Table  1,  Appendix.)  It  will  be 
noticed  that  the  minus  correction  does  not  stop  at 
32°,  but  extends  down  to  28°  (—2  C.),  since  the  scale 
in  general  use,  and  considered  the  best,  is  of  brass, 
and  its  inches,  which  have  their  true  length  at  a  tem- 
perature of  62°,  are  too  short  at  32°,  owing  to  the  con- 
traction of  the  metal.  If  the  scale  is  of  glass,  iron,  or 
wood,  different  corrections  are  required,  depending  on 
the  different  coefficients  of  expansion. 

CORRECTION  FOR  ALTITUDE  OR  REDUCTION  TO  SEA- 
LEVEL. 

As  we  ascend  in  the  atmosphere  the  air  pressure 
gradually  diminishes  and  the  barometer  reads  lower. 
In  order  to  make  barometer  readings  comparable  at 
stations  of  different  elevation,  it  is  necessary  to  reduce 
them  to  a  common  plane — usually  the  sea-level.  This 
reduction  depends  upon  the  temperature  of  the  outside 
air  as  well  as  the  height  of  the  station.  It  is  impor- 
tant to  obtain  accurately  the  elevation  of  the  barometer 


12  AMERICAN  WEATHER. 

t 

above  sea-level.  If  it  is  impossible  to  get  the  correct 
elevation,  an  approximate  value  may  be  computed  by 
means  of  barometric  observations  at  the  station  com- 
pared with  those  made  at  the  same  time  at  a  neighbor- 
ing station,  the  elevation  of  which  is  known.  Table 
No.  2  gives  the  reduction  for  barometer  readings  at 
stations  up  to  1500  feet. 

The  mercury  in  the  Fortin  barometer  is  liable,  in 
course  of  time,  to  oxidation.  The  instrument  can  be 
safely  inverted  and  the  cistern  opened  by  a  skilled  and 
careful  person.  The  oxide  is  readily  separated  by 
means  of  a  cone  of  clean  white  paper,  the  pure  mercury 
passing  readily  through  the  tiny  hole  at  the  apex. 

Barometers  should  never  be  moved,  even  a  few  feet, 
except  after  screwing  up  the  cistern  until  the  mercury 
quite  touches  the  top  of  the  tube.  The  instrument  can 
then  be  safely  inverted  and  with  moderate  care  trans- 
ported, without  injury,  to  any  distance.  After  such 
removals  the  vacuum  should  be  tested.  If  it  is  quite 
perfect  and  free  from  moisture  and  air,  the  mercury 
when  the  tube  is  suddenly  tipped  strikes  the  top  with 
a  sharp,  clear  sound. 


An  inverted  siphon  tube  filled  partly  with  air  and 
partly  with  glycerine,  called  the  sympiesometer,  was 
formerly  much  in  use  as  a  cheap  weather  glass.  Its 
indications  are  uncertain  and  untrustworthy,  while  the 
instrument  easily  becomes  unserviceable,  so  that  it  is 
now  rarely  used. 

THE  ANEROID   BAROMETER. 

Although  the  mercurial  is  considered  the  standard 
barometer,  yet  aneroid  and  metallic  barometers  have 


AMERICAN  WEATHER.  13 

great  advantages,  owing  to  their  extreme  portability 
and  adaptability  for  self -registration,  and  when  com- 
pensated and  well  made  are  most  valuable  substitutes 
for  the  mercurial  form  of  instrument. 

The  principle  of  the  metallic  (Bourdon's)  barometer 
is  somewhat  similar  to  that  of  the  aneroid.  These  in- 
struments have  come  into  extensive  use,  owing  to  their 
cheapness  and  convenient  method  of  reading.  The 
aneroid  is  especially  suitable  for  seafaring  persons 
employed  in  boats  or  small  vessels,  where  mercurial 
barometers  cannot  be  satisfactorily  used. 

A  small  hermetically  sealed  metallic  box,  from 
which  all  the  air  has  been  exhausted,  and  a  heavy 
spring,  to  which  the  top  of  box  is  attached,  are  the 
principal  parts  of  the  aneroid  barometer.  Its  index 
is  moved  by  a  combination  of  levers  connected  with 
the  top  of  the  vacuum  chamber,  which,  having  a  very 
thin  top,  is  raised  up  by  the  spring  when  the  pressure 
of  the  atmosphere  decreases  and  is  forced  inward  when 
the  pressure  increases. 

The  instruments  are  graduated  experimentally,  as 
they  do  not  measure  pressure  absolutely,  but  afford 
indications  relative  to  a  mercurial  barometer. 

Unfortunately,  even  aneroids  of  the  best  workman- 
ship do  not  remain  accurate,  owing  to  deterioration  of 
the  metals  used.  Either  rust,  corrosion,  or  the  weak- 
ening of  the  springs  or  levers,  resulting  from  a  per- 
manent set,  is  sufficient  to  render  the  readings  errone- 
ous in  time,  while  rough  usage  almost  invariably  does 
so  at  once.  Frequent  comparisons  with  standard  mer- 
curial barometers  are  therefore  necessary  to  insure  the 
continued  accuracy  of  the  aneroid. 

The  importance  and  utility  of  self -registering  mete- 
orological instruments  have  long  been  evident,  and  the 
active  minds  of  inventors  have,  to  a  considerable  de- 


14  AMERICAN  WEATHER. 

gree,  supplied  the  necessary  devices.  The  registering 
instruments  in  common  use  may  be  divided  into  two 
classes  :  mechanical,  where  the  work  is  largely  done 
by  the  action  of  the  element  which  is  to  be  recorded, 
and  electrical,  where  the  mechanical  action  of  the  ele- 
ment recorded  is  simply  confined  to  the  closing  or 
breaking  of  an  electrical  circuit.  Mechanical  instru- 
ments require  a  considerably  greater  expenditure  of 
force  than  electrical,  and  in  consequence  are  not  so 
sensitive,  and  the  record  has  a  tendency  to  lag  upon 
the  actual  march  of  the  instrument. 

Electricity  is  an  important  factor  in  facilitating  auto- 
matic registration,  its  value  depending  on  the  well- 
known  fact  that  an  electric  current,  passing  through 
wires  wound  about  a  piece  of  soft  iron,  makes  the 
metal,  for  the  time  being,  a  magnet,  and  that  a  cessa- 
tion of  the  flow  of  electricity  immediatelydemagnetizes 
the  iron. 

The  registration  of  the  movements  of  the  barometer 
by  photography  to  insure  great  accuracy,  requires  that 
the  temperatures  of  the  attached  thermometer  should 
also  be  photographed.  This  method,  being  cumber- 
some and  costly,  is  very  rarely  used,  since  more  satis- 
factory and  almost  as  reliable  results  can  be  otherwise 
obtained  by  mechanical  or  electrical  means,  whereby 
the  oscillations  of  the  mercury  are  recorded  on  paper 
ruled  to  scale. 

A  number  of  ingenious  devices  in  use  at  European 
observatories  fail  to  commend  themselves  to  general 
use,  since  their  indications  are  marked  upon  plain 
paper,  thus  necessitating  measurements  to  obtain  the 
time  and  height  of  the  barometer. 

Among  the  mercurial  barometers  registering  by  elec- 
tricity, the  most  satisfactory  which  have  fallen  under 
the  writer's  notice  are  Gibbon's,  Hough's,  Eccard's, 


V, 

e" 


Transmitter.  Barometer. 

FIG.  2. — ECCARD'S  TRANSMITTING  BAROMETER. 


AMERICAN  WEATHER.  15 

and  Draper's.  Gibbon's  and  Hough' s  instruments  de- 
pend upon  a  common  principle,  wherein  the  use  of  the 
siphon  form  of  the  barometer  is  necessary.  A  small 
float  in  the  short  arm  of  the  siphon  is  connected  by  a 
thread  with  the  short  arm  of  a  light  pivoted  lever, 
which  has  the  end  of  its  long  arm  separated  about  a 
sixteenth  of  an  inch  from  platinum  points  immedi- 
ately above  and  below  it.  Whether  the  mercury  rises 
or  falls  in  the  short  arm  of  the  siphon,  the  movement 
of  the  float  causes  an  opposite  movement  in  the  direc- 
tion of  the  long  arm  of  the  lever,  which  consequently 
touches  either  the  platinum  point  above  or  below  it. 
The  moment  the  lever  touches  either  platinum  point, 
an  electrical  circuit  is  completed,  and  the  action  of  the 
armature  of  the  magnet  moves  a  ratchet-wheel,  which, 
by  gearing,  raises  or  lowers,  as  the  case  may  be,  the 
counterbalanced  lever  until  it  no  longer  touches  the 
platinum  points  and  the  circuit  is  broken  and  the 
magnet  made  inactive.  At  the  same  time  a  different 
set  of  geared  wheels  raises  or  lowers,  to  the  same  pro- 
portional extent,  a  pencil  which  traces  the  record  on 
an  upright  revolving  cylinder,  to  which  a  paper  with 
an  exaggerated  scale  is  attached.  The  records  obtained 
from  such  instruments  show  in  a  strikingly  graphic 
and  quite  accurate  manner  the  barometric  fluctuations. 
It  is  practicably  impossible,  however,  to  keep  the  mer- 
cury of  the  barometer  at  a  uniform  temperature,  so  that 
for  readings  of  great  accuracy  such  records  are  not 
entirely  satisfactory. 

Eccard's  transmitting  barometer,  Fig.  No.  2,  some- 
times has  a  duplicate  set  of  magnets  and  another  elec- 
tric circuit,  by  means  of  which  a  second  record  is 
made  at  any  convenient  distance. 

The  Draper  self-recording  mercurial  barometer  con- 
sists of  a  glass  tube  in  a  fixed  position,  while  the  cis- 


16 


AMERICAN  WEATHEE. 


U 


FIG.  3. — RICHARD'S  SELF-REGISTERING  ANEROID  BAROMETER. 

tern  or  reservoir  in  which  the  lower  end  of  the  tube 
dips  is  suspended  by  two  steel  springs  with  an  at- 
tached pencil,  which  moves  up  or  down  the  paper 
(which  is  ruled  to  scale)  as  the  mercury  flows  in  or  out 
of  the  tube  when  the  pressure  increases  or  dimin- 
ishes. 

The  "  Richard"  self -registering  aneroid  barometer, 
shown  in  Fig.  3,  consists  of  a  cylinder,  A,  on  which 
the  recording  paper  is  wound,  revolving  once  a  week 
by  means  of  a  clockwork  ;  a  series  of  metallic  boxes, 
B,  eight  in  number,  screwed  together  and  exhausted  of 
air  ;  a  compound  lever,  by  means  of  which  the  motion 
of  the  top  of  the  metallic  boxes  is  transmitted,  magni- 
fied about  forty  times,  to  the  marking  pen,  C.  As  far 
as  vacuum  is  concerned  the  shells  are  independent  of 
each  other. 

The  instrument  is  compensated  for  temperature. 
This  is  accomplished  by  leaving  a  sufficient  quantity 


AMERICAN   WEATHER.  17 

of  air  in  one  of  the  shells,  ascertained  by  experiment 
when  the  instrument  is  made,  so  that  with  a  rise  of 
temperature  the  tendency  of  the  barometer  to  register 
too  low  on  account  of  the  expansion  of  the  levers  and 
other  parts  is  counteracted  by  the  increased  pressure 
of  the  air  in  the  shell.  The  instrument,  however, 
should  be  kept  at  a  uniform  temperature. 

The  cylinder  can  be  turned  and  adjusted  within  small 
limits,  so  as  to  make  the  time  scale  correct  by  lifting  it 
up  after  loosening  the  nut  inside  of  it.  The  paper  is 
ruled  horizontally  0.05  of  an  inch  apart,  and  the  read- 
ings can  be  made  to  the  nearest  hundredth. 

When  the  sheet  is  to  be  changed  the  pen  is  released 
from  contact  with  the  paper  by  pushing  the  lever,  D, 
to  the  right. 

When  the  instrument  is  first  set  up  at  a  place,  or  a 
new  sheet  is  put  on,  the  pen  is  made  to  mark,  within 
0.02  inch,  the  pressure  at  the  place,  corrected  for  tem- 
perature and  instrumental  error.  This  adjustment  is 
made  by  raising  or  lowering  the  whole  series  of  aneroid 
boxes  by  means  of  a  key.  This  adjustment  is  apt 
in  time  to  change  a  little,  there  being  a  constant  ten- 
dency for  an  aneroid  barometer  to  read  too  high. 

The  mean  daily  pressure  is  obtained  from  twenty- 
four  hourly  observations.  The  diurnal  variation  of 
the  barometer  is  so  great  and  varies  so  from  local 
causes,  as  will  be  shown  in  a  later  chapter,  that  a  long 
series  of  observations  is  necessary  to  determine  the 
corrections  to  be  made  in  order  to  reduce  the  readings 
of  any  hour  to  the  true  daily  mean.  In  table  No.  3 
will  be  found  approximate  corrections  to  reduce  such 
readings  in  the  United  States. 


CHAPTER  III. 

TEMPERATURE  OF  THE  AIR. 

THE  temperature  of  the  air  is  not  only  scientifically 
the  most  important  meteorological  element,  but  it  is 
also  the  one  which  most  strongly  affects  the  comfort 
and  appeals  to  the  attention  of  mankind.  The  ther- 
mometers in  common  use  for  obtaining  air  temperature 
are  of  spirits  (alcohol)  or  mercury,  and  are  known  as 
dry  (or  standard),  wet,  maximum  and  minimum. 

Thermometers  sold  at  a  low  price,  without  the  name 
of  a  trustworthy  maker,  should  not  be  used  for  exact 
observations.  Many  cheap  instruments  have  the  scales 
made  on  a  uniform  pattern,  the  tube  being  attached 
thereto  so  that  some  single  point  of  its  scale  may  coin- 
cide with  the  correct  degree  mark.  Not  infrequently 
the  errors  of  these  thermometers  are  not  greater  than 
one  or  two  degrees  at  temperatures  between  32°  and 
60°,  but  owing  to  constrictions  or  irregularities  in  the 
diameter  of  the  bore,  the  errors  often  are  as  great  as 
five  or  even  ten  degrees  at  temperatures  below  zero, 
or  above  100°. 

Mercury  presents  most  obvious  advantages  for  ther- 
mometric  use,  since  its  qualities  are  such  that  little 
heat  derived  from  exterior  sources  is  absorbed,  while 
almost  the  entire  amount  is  rapidly  transmitted  and 
expands  the  entire  mass.  In  other  words,  mercury  has 
high  conductivity,  low  specific  heat,  and  a  nearly  con- 
stant coefficient  of  expansion  through  about  seven 
hundred  degrees,  its  range  of  fluidity.  Below  the 


AMEKICAN   WEATHER.  19 

point  at  which  mercury  freezes  (—37.9°  F.,  as  deter- 
mined by  the  late  Dr.  Balfour  Stewart),  it  is  necessary 
to  nse  other  thermometers — generally  those  filled  with 
pure  alcohol  or  spirits  of  wine.  The  use  of  spirit  ther- 
mometers is  not  recommended  except  at  low  tempera- 
tures and  for  minimum  readings,  since  the  spirits  of 
wine  acquires  the  temperature  of  the  air  slowly,  and 
its  coefficient  of  expansion  is  somewhat  irregular. 
Chloroform,  ether,  and  bisulphide  of  carbon  have  been 
suggested  as  possibly  suitable  substitutes  for  alcohol, 
as  a  thermometric  fluid. 

For  temperatures  above  —35°  (F.)  the  mercurial  ther- 
mometer is  preferable.  It  should  have  a  small  cylin- 
drical bulb,  with  sufficiently  small  tube  to  allow  of  a 
long  enough  scale  to  be  graduated  for  the  greatest  pos- 
sible range  of  temperature  in  the  locality  where  it  is  to 
be  used.  In  general,  north  of  the  39th  parallel  in  the 
United  States  the  scale  should  be  graduated  from  —38° 
to  115°,  while  to  the  southward  of  that  parallel  the 
range  should  be  from  —20°  to  130°. 

The  thermometer  bulb  should  be  filled  two  years  be- 
fore being  used,  so  that  the  molecular  changes  in  the 
glass,  which  are  so  productive  of  errors,  should  take 
place  before  the  graduation.  The  instrument  should 
be  tested,  after  filling,  at  some  recognized  observatory, 
and  the  errors  should  be  determined  for  every  ten  de- 
grees from  92°  to  —37.9°  (F.),  the  temperature  of  freez- 
ing mercury.  Thermometers  of  the  United  States  Sig- 
nal Service  are  usually  tested  from  102°  to  —28°,  but 
for  special  alcohol  thermometers,  for  use  at  inland 
northern  stations,  the  tests  are  carried  to  —58°.  The 
best  thermometers  should  not  have  errors  greater  than 
0.3°,  nor  should  the  change  of  error  in  ten  consecutive 
degrees  be  greater  than  this. 

Errors  arise  from  the  bore  changing  its  diameter  from 


20  AMERICAN  WEATHEK. 

point  to  point,  unless  suitable  allowance  is  made  for  this 
in  the  graduation,  by  putting  the  marks  closer  together 
in  some  places  and  farther  apart  in  others.  This  proc- 
ess is  called  calibration.  A  small  part  of  the  contents 
of  the  tube  is  made,  while  at  a  constant  temperature, 
to  occupy  different  parts  of  the  tube.  Its  varying 
lengths  in  different  places  indicate  how  the  graduations 
should  vary. 

The  "  freezing  point"  (32°)  of  a  mercurial  thermome- 
ter continually  changes,  although  slightly,  rising  with 
age  and  lowering  after  exposure  to  unaccustomed  high 
temperatures.  Mercurial  thermometers  eight  years  old 
have  been  found  to  have  the  freezing  point  0.6°  too 
high,  the  greater  part  of  the  changes  probably  occur- 
ring the  first  year. 

The  necessity  of  comparisons  is  shown  by  the  fact 
that  many  expensive  alcohol  thermometers  from  a 
maker  of  high  reputation  have  been  found  to  read 
four  or  more  degrees  too  low  at  —30°,  and  in  one 
instance  twelve  degrees  too  low  at  —58°.  One  case 
is  known  where  a  mercurial  thermometer  with  a  Kew 
certificate  read  two  and  one  tenth  degrees  high  at  62°, 
and  an  alcohol  instrument  of  American  manufacture 
read  over  twenty  degrees  too  low  at  —60°. 

The  depression  of  the  freezing  point  of  a  thermome- 
ter from  exposure  to  unusually  high  temperatures,  say 
212°,*  range  from  0.1°  to  0.8°,  being  greatest  when  the 
glass  contains  about  14  per  centum  of  potash  and  the 
same  amount  of  soda,  and  least  when  either  of  the 
foregoing  constituents  is  entirely  replaced  by  lime. 
This  depression  is  temporary,  and  the  instrument  slowly 
recovers  its  normal  condition,  the  return  being  the 


*  Somewhat  above  212°,  however,  the  action  reverses,  and  at  630" 
(350°  C.)  the  freezing  point  is  raised  from  12°  to  24°. 


AMEKICAN  WEATHEK.  21 

more  rapid  as  the  tube  is  older.  Conversely,  exposure 
to  unusually  low  temperatures  raises  this  freezing 
point,  though  very  slightly,  —30°  only  two  tenths. 

The  temperature  of  melting  ice  diminishes  very 
slightly  with  increasing  pressure,  about  one  degree  F. 
only  for  sixty  atmospheres.  But  the  mechanical  effect 
of  sixty  atmospheres  on  the  bulb  would  be  to  increase 
the  readings  of  a  thermometer  about  thirty  degrees. 

To  test  thermometers  at  temperatures  above  32°  (zero 
C.)  water  should  be  used  ;  from  32°  to  —40°  alcohol 
cooled  by  surrounding  mixture  of  ice  and  salt,  or  ice 
and  muriatic  acid  or  liquid  ammonia.  At  tempera- 
tures below  —40°  the  cooling  is  effected  by  liquefied 
nitrous  oxide. 

Two  thermometric  scales  are  in  common  use,  Fahren- 
heit and  Centigrade  (Celsius),  while  that  of  Reaumer 
has  been  extensively  used  in  the  near  past. 

The  Reaumer  graduation,  in  which  80°  marked  the 
interval  from  zero  at  melting  ice  to  80°  at  the  boiling 
point,  is  now  rarely  used.  For  convenience  of  conver- 
sion it  is  stated  that  four  degrees  Reaumer  equals  five 
degrees  Centigrade,  or  nine  degrees  Fahrenheit.  In 
converting,  it  should  be  borne  in  mind  that  the  zero  of 
Reaumer  corresponds  to  32°  Fahrenheit. 

The  Centigrade  scale  is  in  general  use,  except  in 
English-speaking  countries  where  Fahrenheit  is  em- 
ployed. Zero  Centigrade  represents  melting  ice,  gen- 
erally known  as  the  freezing  point,  while  the  boiling 
point  of  water  marks  100°.  In  the  Fahrenheit  scale 
these  two  points  represent  respectively  32°  and  212°.* 


*  The  boiling  point  of  Fahrenheit's  thermometer  is  very  slightly  lower 
than  the  boiling  point  on  the  Centigrade  scale,  since  the  former  is  based 
on  an  atmospheric  pressure  of  29.905  inches  at  London,  and  the  latter 
one  of  760  mm.  (29.922  inches)  at  Paris.  Reduced  to  standard  gravity 


22  AMERICAN  WEATHER. 

To  convert  Fahrenheit  readings  into  Centigrade, 
subtract  32,  multiply  the  remainder  by  5,  and  divide 
the  product  by  9.  To  convert  Centigrade  to  Fahren- 
heit multiply  by  9,  divide  the  product  by  5,  and  add  to 
the  result  32. 

All  readings  below  the  zero  of  these  three  scales  are 
prefixed  by  a  minus  sign.  Since  the  zero  point  of  the 
Centigrade  thermometer  coincides  with  frost,  or  the 
freezing  point,  it  is  common  in  Europe  to  speak  of  the 
minus  readings,  Centigrade,  as  so  many  degrees  of 
" frost."  From  this  convenient  method  has  arisen  an 
inaccurate  one  in  England  of  classing  readings  on  the 
Fahrenheit  scale  in  a  similar  manner,  so  that  at  times 
it  is  doubtful  whether  the  person  using  the  term  has 
in  mind  a  reading  that  number  of  degrees  below  the 
freezing  point  or  below  zero  Fahrenheit.  The  zero  of 
Fahrenheit  marks  a  quite  indefinite  point,  being  thirty- 
two  divisions  on  that  scale  below  the  freezing  point, 
and  is  generally  supposed  to  indicate  the  degree  of 
cold  obtained  by  mixing  snow  and  salt.  A  tempera- 
ture of  — 6.5°  F.  can,  however,  be  thus  produced. 

The  standard  of  32°  Fahrenheit  is  the  temperature 
of  pure  melting  ice  ;  and  of  212°  that  of  steam  from 
pure  water  boiling  under  a  pressure  of  (760  mm.)  29.922 
inches  of  mercury. 

The  small  size  of  its  degrees  and  the  comparative 
freedom  of  its  readings  from  minus  signs  are  the  de- 
cided advantages  of  the  Fahrenheit  scale. 


SELF-REGISTERING  THERMOMETERS. 

The  highest  and  lowest  air  temperatures  occur  at  irreg- 
ular hours  and  continue  but  a  brief  time,  and  to  insure 


(45°  of  latitude),  these  two  readings  would  be  respectively  29.923  and 
29.932  inches. 


AMERICAN  WEATHER.  23 

a  record  of  these  important  phases  of  heat  special  in- 
struments have  been  devised. 

The  most  important  of  self -registering  thermometers 
is  the  minimum,  since  the  lowest  temperature  usually 
occurs  at  night,  slightly  before  dawn,  and  so  is  less 
likely  to  be  observed.  Six,  in  1781,  devised  the  first 
self  registering  thermometer,  which  recorded  both  the 
maximum  and  minimum  temperatures.  The  action 
of  Six's  instrument  (which  is  U-shaped)  depends  on 
the  expansion  of  a  considerable  quantity  of  alcohol  in 
one  arm  which  displaces  a  U-shaped  column  of  mercu- 
ry when  the  temperature  rises,  while  the  contracting 
spirit  during  falling  temperature  permits  the  pressure 
of  air  in  the  top  of  the  other  arm  to  cause  a  movement 
of  the  mercury  in  the  reverse  direction.  The  moving 
column  of  mercury  displaces  movable  indices,  which 
thus  indicate  the  highest  and  lowest  temperatures. 
The  instrument  is  used  now  somewhat  in  Great  Britain, 
and  more  rarely  in  the  United  States,  since  its  indica- 
tions are  not  strictly  accurate,  and  it  easily  gets  out  of 
order  in  transportation. 

The  minimum  thermometer  of  the  pattern  devised  by 
Rutherford  is  to-day  the  accepted  standard,  and  is  in 
very  general  use.  In  this  thermometer  there  is  im- 
mersed in  the  spirits  of  wine  a  small  steel  index,  the 
simple  weight  of  which  is  so  slight  that  the  liquid, 
contracting  in  the  tube,  does  not  separate  and  leave  dry 
the  index,  but  drags  it  back,  its  upper  end  remaining 
tangent  to  the  end  of  the  receding  column  of  alcohol. 
When  the  temperature  rises,  the  expanding  fluid  passes 
freely  by  the  index,  and  its  upper  end  remains  at  the 
point  of  lowest  temperature.  The  thermometer  is  set 
by  raising  the  bulb  slightly  so  that  the  index  may 
move  gently  to  the  top  of  the  column. 

This  thermometer,  in  common  with  all  spirit  ther- 


24  AMERICAN  WEATHER. 

mometers,  is  subject  to  serious  errors,  owing  to  the 
upper  part  of  the  spirit  column  evaporating  and  rising 
to  the  top  of  the  tube,  where  it  condenses  and  remains 
detached.  This  separation  of  the  column  frequently 
occurs,  and  while  the  detached  part  measures  ordi- 
narily but  one  or  two,  yet  its  value  occasionally 
amounts  to  ten  or  even  fifteen  degrees.  Observers 
should  not  only  carefully  and  daily  examine  the  spirit 
thermometers  to  guard  against  this  error,  but  should 
regularly  compare  the  current  readings  with  mercurial 
instruments,  since  the  colorless  character  of  spirits  of 
wine  renders  detection  of  detached  parts  somewhat 
difficult.  The  writer  was  once  called  upon  by  an  in- 
telligent observer  to  examine  his  minimum  thermome- 
ter (a  standard  instrument),  which,  he  complained,  al- 
ways read  lower  than  the  Signal  Service  instrument 
near  by,  and  to  explain  the  cause  of  discrepancy.  The 
observer  was  much  chagrined  when  a  detached  section 
of  spirit,  equal  to  three  or  four  degrees  upon  the  scale, 
was  pointed  out  to  him  at  the  top  of  the  tube.  It  would 
be  a  decided  check  to  this  source  of  error  if  a  marked 
coloring  matter  could  be  introduced  as  a  permanent 
and  unchanging  part  of  the  spirits  of  wine,  but  unfor- 
tunately the  red  coloring  matter,  occasionally  used, 
separates  from  the  fluid,  thus  introducing  another 
source  of  error. 

Whenever  the  column  of  spirit  is  broken  into  de- 
tached portions,  or  the  index  has  been  forced  out  of 
the  fluid,  the  thermometer  can  generally  be  restored 
to  good  condition  by  swinging  it  quickly,  but  steadily, 
bulb  downward,  until  the  entire  column  unites.  When 
this  course  fails,  the  detached  bits  of  spirit  are  some- 
times united  by  tapping  the  instrument  quite  sharply 
on  the  hand  or  some  other  elastic  body.  As  a  final 
resort  the  thermometer  may  be  immersed  in  water 


AMERICAN   WEATHER.  25 

which  should  be  very  gradually  heated  until  the  spirit 
completely  unites.  The  two  latter  methods  should  be 
resorted  to  only  in  extreme  cases,  and  the  last  process 
followed  with  great  caution,  lest  the  instrument  break 
from  the  expansion  of  the  alcohol. 

Minimum  thermometers  with  cylindrical  bulbs  are 
generally  recommended ;  spherical  bulbs  take  the 
temperature  of  the  air  too  slowly,  owing  to  the  com- 
paratively small  exposed  surface,  while  bulbs  of  such 
shape  as  to  present  to  the  air  very  large  surfaces,  and 
thus  enhance  the  instrument's  sensibility,  are  gener- 
ally so  fragile  as  to  be  out  of  place,  except  in  the  hands 
of  the  most  skilled  observers. 

One  source  of  error  in  the  reading  of  the  Rutherf  ord 
minimum  is  the  displacement  of  the  index  by  high 
winds  or  other  disturbing  causes.  This  source  of 
error  is  guarded  against  in  Baudin's  vertical  minimum 
thermometer,  d  marteau.  *  This  thermometer  is  placed, 
like  an  ordinary  instrument,  in  a  vertical  position. 
The  index  terminates  at  each  end  in  spherical  glass 
balls.  A  delicate  spring  with  one  end  free  is  attached 
to  the  index,  and  is  so  arranged  that  its  pressure 
against  the  tube  keeps  the  index  in  a  fixed  position. 
The  spring,  however,  is  not  so  strong  as  to  prevent  the 
film  of  the  contracting  column  of  alcohol  from  drawing 
the  index  downward  when  the  temperature  falls.  The 
thermometer  is  set  by  turning  it  bulb  upward  when  a 
light  enamel  rod  in  the  bulb  of  the  thermometer  de- 
scends the  bore  and,  acting  as  a  hammer,  forces  the 
index  to  the  end  of  the  column  of  alcohol.  This  ther- 
mometer is  highly  recommended. 

There  are  several  devices  for  registering  the  highest 


*  The  name  of  the  thermometer  d  marteau  refers  to  the  rod  used  in 
setting  it. 


26  AMERICAN   WEATHER. 

temperature  attained  by  the  air.  In  Rutherford's 
maximum  the  expanding  mercury  pushes  before  it  a 
light  porcelain  index,  which  remains  at  the  highest 
point  until  it  is  reset  by  placing  the  instrument  upright 
and  allowing  the  index  to  drop  to  the  mercury.  This 
instrument  is  not  much  used. 

The  Phillips  maximum  has  a  bubble  of  air  intro- 
duced into  the  column,  about  an  inch  from  the  upper 
end,  which  is  thus  detached.  When  the  mercury  con- 
tracts the  detached  end  remains  fixed,  and  thus,  serv- 
ing as  an  index,  marks  the  highest  temperature.  This 
instrument  is  falling  into  disuse,  since  the  air  bubble 
is  readily  displaced,  either  by  rough  handling  during 
transportation  or  by  the  mercury  being  withdrawn 
into  the  bulb  by  lower  temperatures  than  the  instru- 
ment registers. 

The  maximum  thermometer  most  in  use  is  somewhat 
after  the  pattern  devised  by  Negretti  and  Zambra. 
Just  above  the  bulb  there  is  a  slight  constriction  in  the 
tube  through  which  the  expanding  mercury  is  forced, 
but  which  causes  the  column  to  break  when  the  mer- 
cury begins  to  contract.  The  column  remains  at  the 
highest  point  until  the  thermometer  is  set  by  detach- 
ing the  suspension  pin  and  whirling  the  thermometer 
around  the  pin,  which  passes  through  its  upper  end. 

The  Richard  self-registering  thermometer,  shown  in 
Fig.  4,  has  many  parts  similar  to  the  self-register- 
ing aneroid.  The  essential  or  thermometric  part  is 
the  copper  bulb,  A,  filled  with  alcohol. 

As  the  temperature  fluctuates,  increasing  or  dimin- 
ishing the  volume  of  alcohol,  the  curvature  of  this 
crescent-shaped  bulb  changes.  The  motion  of  the  free 
end  is  transmitted  by  a  compound  lever  to  the  marking 
pen.  When  the  instrument  is  set  up  or  the  sheet  re- 
newed, once  a  week,  the  pen  should  be  made  to  register 


AMERICAN   WEATHER. 


the  same  as  the  dry  thermometer.  This  adjustment  is 
made  by  means  of  the  nut  at  <?,  turning  it  so  as  to  raise 
or  lower  the  pen. 


FIG.  4. — RICHARD'S  REGISTERING  THERMOMETER. 

The  Draper  self -registering  thermometer  is  a  metallic 
instrument,  wherein  strips  of  steel  and  brass  (see  Fig. 
5)  about  12  inches  long  are  soldered  together.  The 
difference  in  their  expansion  causes  changes  in  the  cur- 
vature of  the  strip,  one  end  of  which  is  fixed.  The 
movements  of  the  other  end,  by  a  simple  device,  pro- 
duce the  motion  of  a  registering  pen.  There  are  two 
of  these  compound  strips,  so  arranged  as  to  curve  in 
opposite  directions  as  the  temperature  changes.  They 
act  on  opposite  sides  of  the  pivot  of  the  marking  pen, 
in  order  to  insure  greater  accuracy  in  the  record  when 
the  temperature  is  fluctuating. 

The  record  being  traced  on  a  disk,  the  fluctuations 
for  a  whole  week  can  be  seen  at  once.  The  disk  hold- 
ing the  record  paper  is  made  to  revolve  by  clockwork 
once  a  week.  The  indications  of  the  instrument  are 
generally  trustworthy  to  within  two  degrees  F. 


28 


AMERICAN  WEATHER. 


FIG.  5. — DRAPER'S  REGISTERING  THERMOMETER. 


THERMOMETER   EXPOSURE. 

The  question  of  the  immediate  environment  of  the 
thermometer  is  a  most  important  consideration.  "  Full 
and  free  natural  ventilation  is  essential,  and  rain  should 
be  excluded.  Provision  should  be  made  against  heat 
from  direct  solar  radiation  or  that  reflected  and  radi- 
ated from  surrounding  objects,  especially  from  warm 
walls,  chimneys,  etc. 

While  a  fixed  instrument  shelter  is  convenient,  and 
for  self -registering  instruments  indispensable,  yet  most 
accurate  single  temperature  readings,  both  of  dry  and 


AMERICAN  WEATHER.  29 

wet  thermometers,  are  obtainable  by  another  method. 
It  consists  in  the  use  of  dry  and  wet  bulb  thermometers 
fastened  together  and  quite  rapidly  whirled  by  a 
string,  held  in  the  hand  or  otherwise.  The  observer 
should  stand  in  an  open  space  where  there  is  good 
ventilation  and  be  shaded  from  the  sun. 

The  rapidly  varying  heat  phases  of  the  air,  conse- 
quent on  convection,  radiation,  and  reflection,  make  it 
difficult  to  so  place  a  thermometer  as  to  insure  its  in- 
dicating the  true  temperature  of  the  air.  The  pattern 
and  material  of  the  shelter,  with  its  freedom  from  sur- 
rounding objects,  which  unduly  reflect  or  radiate  heat, 
as  well  as  the  height  of  the  thermometer  above  the 
ground,  are  conditions  which  more  or  less  materially 
affect  the  correct  reading  of  thermometers  used  to  de- 
termine the  temperature  of  the  air.  It  was  once  the 
experience  of  the  writer  in  investigating  the  cause  of 
unduly  high  temperatures,  recorded  by  a  thermometer 
apparently  well  placed  in  a  standard  louvre  shelter, 
that  the  disturbing  element  was  a  painted  tin  roof, 
some  fifty  feet  distant.  This  roof,  reflecting  the  sun's 
heat  at  an  obtuse  angle,  raised  the  temperature  at 
times  from  two  to  three  degrees. 

A  thermometer  shelter  should  have  double  roofs  six 
or  eight  inches  apart,  a  solid  bottom,  which  should  be 
hinged,  so  it  can  be  closed  or  not,  and  sides  of  blind  or 
louvre  work.  The  slats  of  the  sides  should  slope  at 
an  angle  of  45°  and  be  quite  close  together.  When 
practicable,  the  shelter  should  be  from  eight  to  ten  feet 
above  the  sod  or  the  roof,  in  the  latter  case  having  a 
large  wooden  platform  beneath  it.  When  a  window 
shelter  is  necessary,  it  should  be  on  the  north  side,  and 
as  open  as  possible,  care  being  taken  to  barely  protect 
the  thermometer  from  the  effects  of  the  sun  and  from 
rain.  Openness  of  shelter  thus  tends  to  counteract 


30 


AMERICAN  WEATHER. 


FIG.  6.— DRY  AND  WET  THER- 
MOMETERS, MOUNTED. 


AMERICAN  WEATHER.  31 

the  effect  of  the  temperature  of  the  wall,  which  is  too 
cool  by  day  and  too  warm  at  night. 

The  wet  thermometer  is  only  a  dry  bulb  covered 
with  soft  muslin  well  wet  with  rain  or  clear  water, 
drawn  from  an  attached  cup  or  cistern  by  a  wick.  The 
muslin  should  be  kept  in  good  order,  always  clean,  so 
that  the  water  will  be  fully  drawn  from  the  cistern  and 
the  bulb  kept  wet.  Headings  below  32°  require  care 
and  watchfulness,  since  the  bulb  must  be  skilfully 
covered  with  a  thin  coating  of  ice  and  well  ventilated, 
so  that  evaporation  may  take  place  normally  and 
speedily. 

The  arrangement  and  relative  position  of  dry  and 
wet  thermometers  is  shown  by  Fig.  6. 

Artificial  ventilation,  unnecessary  if  there  is  wind, 
becomes  quite  an  important  adjunct  in  calm  weather. 
It  is,  perhaps,  best  obtained  by  rotating  the  ther- 
mometer by  a  whirling  apparatus,  fan  or  bellows 
worked  by  some  simple  mechanical  device  ;  but  when 
these  are  not  convenient  a  fan  moved  by  hand  will  an- 
swer the  purpose.  It  may  be  added  that  this  is  the  most 
difficult  meteorological  observation  to  make  satisfac- 
torily, and  that  trivial  defects  or  slightly  inaccurate 
readings  destroy  completely  its  usefulness.  It  is, 
however,  a  most  important  observation  for  agricul- 
turists, especially  at  the  time  of  early  or  late  frosts. 

Maximum  and  minimum  thermometers  are  often 
conveniently  mounted  together  on  a  small  base  board 
(see  Fig.  No.  7),  which  is  easily  fastened  in  the  in- 
strument shelter  or  other  suitable  place.  The  mini- 
mum should  be  mounted  nearly  horizontal  and  the 
maximum  with  its  bulb  slightly  inclined  downward. 
The  minimum  is  set  by  lifting  up  the  bulb  till  the  in- 
dex drops  to  the  end  of  the  alcohol  column.  In  set- 
ting the  maximum,  remove  the  pin,  thus  allowing  the 


AMERICAN  WEATHEE. 


AMERICAN   WEATHEK.  33 

thermometer  to  drop  in  a  vertical  position.  The  mer- 
curial column  usually  unites  at  a  single  tap,  but  if  it 
does  not  the  instrument  must  be  revolved  rapidly  on 
the  screw  that  secures  it  to  the  board. 

The  observations  made  from  standard  instruments 
in  properly  exposed  situations  are  of  little  practical 
or  theoretical  value  until  they  have  been  grouped,  re- 
duced, and  collated,  so  as  to  give  means  or  averages  for 
comparison  and  discussion. 

The  fluctuations  of  the  temperature  of  the  air  are  so 
continuous,  and  occasionally  so  rapid  and  marked, 
that  even  observations  every  ten  or  fifteen  minutes 
would  not  give  an  absolutely  correct  mean  of  the  day. 

The  average  of  twenty-four  observations,  taken  at 
hourly  intervals,  is,  however,  by  common  consent,  as- 
sumed to  be  the  true  mean  temperature  of  a  day.  To 
obviate  the  necessity  of  taking  even  so  many  observa- 
tions, other  methods  have  been  elaborated,  by  which 
comparatively  correct  daily  means  are  obtained.  These 
methods  are  :  First.  From  readings  of  maximum  and 
minimum  self -registering  thermometers,  a  mode  entail- 
ing little  labor.  Half  of  the  sum  of  these  two  readings 
gives  a  mean  slightly  inaccurate— it  generally  being  a 
little  higher,  less  than  a  degree  above  the  true  mean. 
Corrections  necessary  to  approximately  reduce  this  to 
the  true  mean  have  been  calculated  for  the  various 
months  and  different  parts  of  the  United  States,  which 
are  given  in  Table  No.  4. 

Second.  From  observations  at  a  selected  hour.  At 
New  Haven,  Conn.,  for  instance,  according  to  Loomis, 
the  temperature  at  8.45  A.M.  or  7.45  P.M.  coincides  with 
the  mean  temperature  of  the  day.  This  critical  hour 
varies  not  only  in  localities,  but  also  for  the  month. 
It  can  be  determined  only  from  a  long  series  of  obser- 
vations, and  so  cannot  be  generally  adopted. 


34  AMERICAN   WEATHER. 

Third.  From  observations  at  any  two  hours  of  the 
same  name.  While  the  mean  of  such  similar  hours, 
as  9  A.M.  and  9  P.M.,  differs  but  slightly  from  the  true 
mean,  yet  it  requires  a  series  of  observations  to  select 
hours  when  the  error  is  but  a  few  tenths  of  a  degree. 
At  New  Haven  the  daily  mean  thus  deduced  from  ob- 
servations at  10  A.M.  and  10  P.M.  is  only  about  one 
third  of  a  degree  too  low. 

Fourth.  From  three  daily  observations  at  equal  or 
nearly  equal  intervals.  The  average  of  any  three  such 
hours  varies  but  little  from  the  true  mean  of  the  day. 
It  has  been  found,  however,  that  the  most  satisfactory 
method  for  all  varieties  of  climate  is  obtained  from  ob- 
servations at  7  A.  M.  ,  2  P.  M.  ,  and  9  P.  M.  While  the  mean 
of  these  observations  is  a  little  too  great,  this  error  is 
substantially  eliminated  by  adding  the  9  o'  clock  obser- 
vation twice  to  the  other  observations,  and  dividing 
the  sum  by  four.  This  method  is  strongly  recom- 
mended to  observers. 

The  monthly  mean  is  obtained  from  the  daily  means. 
The  annual  mean  temperature  is  usually  found  by  tak- 
ing the  average  of  all  the  monthly  temperatures  for 
the  year  ;  but  this  process  causes  a  slight  error,  by  giv- 
ing equal  weight  to  months  of  unequal  length.  For 
very  exact  work,  the  preferable  way  is  to  obtain  the 
annual  mean  directly  from  the  daily  averages  of  the 
whole  year.  The  annual  mean  varies  from  year  to 
year,  and  the  mean  temperature  of  a  place  is  the  aver- 
age obtained  from  a  series  of  years — twenty  or  more. 


CHAPTER  IV. 

EADIATION. 

BEFORE  proceeding  to  treat  the  subject  of  aqueous 
vapor,  it  will  be  advisable  to  touch,  on  radiation, 
through  the  action  of  which  such  great  changes  are 
wrought  in  the  temperature  of  the  air  and  in  the  con- 
dition of  aqueous  vapor  itself. 

Radiation  is  the  propagation  of  heat  from  a  warm 
body  through  space.  The  transmission  takes  place  in 
straight  lines.  The  radiation  from  the  earth  is  called 
terrestrial  radiation  ;  that  from  the  sun  solar  radiation. 
The  temperature  at  the  earth's  surface  depends  entirely 
on  these  two  processes.  The  amount  of  heat  coming 
to  the  surface  of  the  earth  from  the  interior  or  that 
received  from  other  stellar  bodies  than  the  sun  is  not 
enough  to  appreciably  affect  bur  climate. 

Our  knowledge  of  the  amount  of  heat  received  by 
the  earth  from  the  sun  is,  as  yet,  very  uncertain,  the 
instrumental  means  so  far  devised  for  ascertaining  it 
being  very  imperfect  and  giving  widely  varying  re- 
sults. 

The  actinometers  of  Herschel,  Pouillet,  Stewart,  and 
Violle  for  measuring  the  amount  of  solar  radiation  are 
alike  in  principle,  that  the  heat  received  from  the  sun 
plus  that  lost  by  radiation  is  the  true  amount.  The 
thermometer  is  surrounded  by  material  tending  to  pre- 
serve an  equable  temperature.  The  instrument  is  ex- 
posed a  given  time  to  the  sun,  and  its  increment  of 
temperature  noted,  and  later,  after  being  placed  an 


36  AMERICAN   WEATHER. 

equal  time  in  the  open  shade,  the  loss  of  heat  is  noted. 
Pouillet  used  water  around  the  thermometer,  Stewart 
cast  iron,  and  Violle  ice,  the  last  being  doubtless  the 
best.  These  instruments  are  complicated  and  their  use 
difficult.  For  a  detailed  description,  the  reader  is 
referred  to  works  on  physics. 

The  quantity  of  heat  that  will  raise  one  gramme  of 
water  at  a  temperature  of  zero  degrees  centigrade,  one 
centigrade  degree  is  called  a  calorie. 

A  surface  of  one  centimetre  square  exposed  perpen- 
dicularly to  the  sun' s  rays  at  the  top  of  the  atmosphere 
would  receive  in  one  minute  of  time  3.0  calories  (Lang- 
ley).  This  is  the  best  value  for  this  quantity,  so  far 
as  ascertained.  It  is  called  the  solar  constant.  The 
value  found  by  Pouillet  was  1.75. 

This  amount  is  sufficient  in  a  year  to  melt  a  layer  of 
ice  178.6  feet  (54.45  metres)  in  thickness.  A  great  deal 
of  this  heat  is  absorbed  by  the  atmosphere  before  it 
reaches  the  earth,  according  to  Langley,  i  of  the  amount 
when  the  sun  is  in  the  zenith,  and  according  to  Pouil- 
let, i  or  £.  For  other  positions  of  the  sun  than  the 
zenith,  a  greater  part  is  absorbed,  as  the  rays  traverse 
a  greater  thickness  of  the  air  before  reaching  the 
earth's  surface.  Without  this  power  of  the  air  to 
absorb  the  heat,  called  selective  absorption,  the  tem- 
perature at  the  earth' s  surface  would  eventually,  accord- 
ing to  Langley,  not  be  greater  than  —328°  (—200°  C.). 

The  amount  of  heat  that  is  absorbed  at  different 
times  varies  greatly,  depending  on  the  quantity  of 
particles  in  suspension  and  the  amount  of  aqueous 
vapor  in  the  air. 

The  bright  and  black  bulb  thermometers  in  vacua 
afford  a  ready  means  of  measuring  relatively  the 
amount  of  this  heat  that  is  absorbed  at  different  times. 
The  less  the  quantity  of  heat  absorbed  by  the  air,  the 


AMERICAN   WEATHER.  37 

higher  will  be  the  reading  of  the  black  bnlb  thermom- 
eter as  compared  with  the  bright  bulb.  But  this 
affords  by  no  means  an  accurate  measure,  as  the  black 
bulb  readings  vary  for  other  reasons,  the  most  impor- 
tant of  which  are  the  thickness  of  the  lamp-black  with 
which  it  is  covered,  the  size  of  the  bulb,  the  thickness 
end  chemical  nature  of  the  glass  composing  the  en- 
closure, and  the  imperfection  of  the  vacuum. 

The  selection  of  a  pair  of  bright  and  black  bulbs  for 
standards,  with  which  the  errors  of  other  solar  ther- 
mometers are  determined,  affords  in  some  measure  the 
method  of  obtaining  quite  accurate  indications  of  the 
relative  amounts  of  heat  absorbed  by  the  air  at  differ- 
ent times  and  places.  These  thermometers  are  usually 
made  maximum  registering,  and  it  is  customary  to 
take  as  their  indications  the  differences  of  their  great- 
est readings  for  the  day.  When  the  sun  isJ.ow  the 
differences  will  not  be  as  great  as  when  the  sun  is 
higher,  as  in  the  former  case  the  rays  traverse  a  greater 
thickness  of  air  and  more  of  the  heat  is  absorbed  before 
reaching  the  bulb. 

But  the  relation  between  the  thermometer  differ- 
ences and  the  heat  absorbed  is  not  a  simple  one.  A 
slightly  less  amount  of  heat  absorbed  by  the  air  will 
cause  a  very  considerable  increase  in  the  differences. 
As  one  ascends  in  the  air  above  the  level  of  the  sea  the 
reading  of  the  black  bulb  in  vacuo  increases  extraor- 
dinarily when  exposed  to  the  sun. 

Comparatively  few  observations  of  this  character 
have  been  made  in  the  United  States,  but  there  is  every 
reason  to  believe  that  observations  from  such  instru- 
ments in  certain  parts  of  Arizona  and  the  arid  regions 
of  the  West  would  show  temperatures  ranging,  in  ex- 
treme cases,  from  160°  to  180°,  if  not  higher.  It  is 
evident  that  at  elevated  stations  in  dry  districts  of  the 


38  AMERICAN   WEATHEE. 

eartli  the  direct  effect  of  the  sun's  rays  is,  proportion- 
ately, very  much  higher  than  the  true  temperature  of 
the  air,  as  compared  with  localities  near  the  sea  or  in 
more  humid  regions. 

At  Leh,  Ladak,  Thibet  (elevation,  11,500  feet),  the 
air  is  so  clear  and  transparent  that,  according  to  Dr. 
Cay  ley,  "by  simply  exposing  water  in  an  ordinary 
phial,  inked  on  the  outside,  and  placed  within  a  larger 
bottle,  the  contents  boiled  under  the  action  of  the  sun's 
rays."  The  temperature  at  which  water  boils  at  Leh, 
owing  to  the  diminished  atmospheric  pressure,  is  about 
190°.  Scott  is  the  authority  for  saying  that  at  this 
station  solar  thermometers  have  registered  214°,  or 
higher,  but  158.4°,  in  1875,  is  the  highest  temperature 
which  Blanford  gives  in  eight  years.  It  is  probable 
that  the  temperature  of  214°  at  Leh  must  have  been 
from  a  thermometer  under  some  such  conditions  as  the 
water  exposed  by  Dr.  Cayley. 

Langley's  experiments  on  Mount  Whitney  show 
that  very  much  higher  temperatures  are  indicated  by 
thermometers  carefully  protected  from  loss  of  heat 
than  by  black  bulb  in  vacuo.  On  September  19th, 

1881,  Langley  obtained  from  a  sun-thermometer  (black 
bulb),  thus  protected,  a  temperature  of  236°,  while  the 
highest  reading  of  the  black  bulb  in  vacua  was  170°. 

The  highest  temperature  from  such  instruments 
under  ordinary  exposure,  as  far  as  the  writer  has  been 
able  to  gather  from  original  sources,  is  that  reported 
by  Blanford — 196.5° — which  was  recorded  on  June  8th, 

1882,  at  Pachpadra,  India,  elevation,  380  feet.     A  few 
other  cases  of  temperature  above  190°  are  found  in 
Blanford' s  reports,  and  these  temperatures  have  been 
corrected  with  reference  to  a  thermometer  adopted  as 
a  standard  by  the  meteorological  reporter  of  the  Gov- 
ernment of  India,    The  mean  excess  of  maxima  tern- 


AMEKICAK  WEATHER.  39 

peratures  in  the  sun  above  those  in  the  shade  at  Bick- 
aneer,  India,  28°  IS".,  73°  E.,  elevation,  744  feet,  equals 
69.8°  for  the  year  and  74.0°  for  February. 

At  Fort  Conger,  82°  K,  65°  W.,  the  maximum  black 
bulb  averaged  for  thirty  consecutive  days,  from  April 
13th  to  May  12th,  1883,  75.4°  above  the  shaded  ther- 
mometer. As  long  as  the  ground  remained  frozen  and 
the  sea  ice  was  unbroken,  the  solar  radiation  steadily 
increased,  and  the  instant  these  conditions  changed  a 
decrease  began.  Differences  of  80°  or  more  between 
the  maximum  black-bulb  and  shade  thermometer  were 
not  infrequent  at  Fort  Conger,  and  on  May  5th,  1883, 
the  extraordinary  difference  of  95.9°  was  observed. 
On  May  31st,  1883,  a  maximum  reading  of  124.5°  was 
noted — this  reading  being  almost  coincident  with  the 
highest  reading  the  same  year  at  Point  Barrow,  Alaska, 
and  Jan-Mayen  Island — 127°  and  120.8°,  respectively. 
The  highest  reading  ever  noted  at  Fort  Conger — 128°, 
June  6th,  1876 — was  five  days  before  snow  had  melted 
so  that  water  ran  freely. 

The  small  amount  of  aqueous  vapor  in  the  winter  air 
of  the  polar  regions  or  on  elevated  plateaus  and  moun- 
tains permits  the  direct  rays  of  the  sun  to  exercise  a 
powerful  influence  on  surfaces  of  high  absorbing 
powers.  Parry,  at  Igloolik  in  February,  1822,  noted 
snow  melting  on  a  black  surface  with  the  temperature 
of  the  air  at  —19°.  The  story  of  melting  pitch  observed 
by  whalers,  while  ice  was  forming  in  the  shade,  is  more 
striking,  though  really  less  remarkable. 

A  simple  reliable  method  of  measuring  the  sun's 
heat  throughout  the  day  is  especially  desirable,  and 
the  invention  of  a  suitable  instrument  would  be  an 
important  contribution  to  meteorology. 

But  if  the  amount  of  solar  radiation  cannot  be  con- 
veniently and  accurately  measured,  there  is  a  simple 


40  AMERICAN  WEATHER. 

method  of  estimating  the  effect  by  observing  the  dura- 
tion of  sunshine. 

The  Campbell- Stokes  sunshine-recorder  is  a  simple, 
inexpensive  instrument,  which  records  sunshine  quite 
accurately.  A  glass  sphere  acts  as  a  lens,  with  its 
focus  on  a  curved  strip  of  mill-board,  ruled  for  the 
hours,  which  is  burned  as  long  as  the  sun  shines. 
Professor  Marvin,  United  States  Signal  Service,  has 
devised  a  photographic  method  of  registering,  whereby 
a  record  for  a  month  is  obtained  on  a  single  sheet. 

The  effect  of  solar  radiation  naturally  varies  with  the 
absorptive  powers  of  the  surface  on  which  the  sun's 
rays  fall,  being  greatest  on  substances  such  as  lamp- 
black, paper,  etc. ,  and  least  on  polished  metals.  Since 
sandy  soils  have  large  absorptive  powers,  it  is  evident 
why  sandy  desert  regions  attain  such  extreme  temper- 
atures, and  since  so  much  heat  is  used  in  evaporating 
from  surfaces  of  water  and  ice,  lakes  and  the  ocean 
have  comparatively  low  temperatures  as  a  greater  mass 
is  warmed,  the  heat  penetrating  the  water  to  some 
depth,  about  five  hundred  feet. 

Since  the  radiating  power  of  differing  surfaces  is  not 
uniform,  it  follows  that  observations  are  not  compar- 
able unless  the  conditions  are  identical.  As  yet  there 
has  been  no  agreement  between  the  various  meteoro- 
logical services  on  this  point,  and  indeed  but  scanty 
attention  has  been  paid  to  the  subject,  nor  have  con- 
tinuous and  extended  observations  been  made  except 
in  India. 

The  most  important  observations  on  solar  radiation 
ever  made  in  the  United  States,  and  probably  in  the 
world,  were  those  of  Professor  Langley,  on  Mount 
Whitney,  California.* 

*  (See  Professional  Papers,  No.  15,  Signal  Service,   "  Researches  on 
Solar  Heat/'  by  S.  P.  Langley.) 


AMERICAN   WEATHER.  41 

The  result  of  Langley'  s  observations  was  to  show : 

1.  The  value  of  the  solar  constant  was  far  larger  than 
had  been  supposed. 

2.  That  the  amount  of  heat  absorbed  by  the  air  was 
likewise  much  greater  than  had  been  previously  esti- 
mated, and  that  this  latter  absorption  was  of  a  selec- 
tive character,  and, 

3.  In  particular  that  the  absorption  of  the  air  dimin- 
ishes progressively  as  the  wave  length  increases,  up  to 
a  certain  very  long  wave  length — that  is  to  say,  that 
up  to  a  certain  estimated  limit  the  air  becomes  more 
and  more  transparent,  to  the  reddish  rays  and  to  the 
invisible  ones  of  heat.     This  latter  is  the  very  reverse 
of  the  opinion  entertained  prior  to  his  work. 

4.  He  also  showed  that  of  two  like  masses  of  air 
selected  first  at  a  high  elevation,  and  second  at  a  low, 
the  former  absorbs  the  less  heat — that  is  to  say,  that 
the  upper  air  absorbs  less  heat  quite  independently  of 
its  rarity. 

5.  By  means  of  his  sensitive  measuring  device  called 
the  bolometer,  he  discovered  that  solar  heat  waves  of 
at  least  0.003  of  a  millimetre  (probably  more)  were 
transmitted  by  the  air,  a  little  over  0.001  being  the 
longest  heat  wave  that  had  been  before  detected  under 
the  circumstances. 

Terrestrial  radiation,  or  escape  of  heat  into  space,  is  a 
constant  phenomena,  which  plays  a  very  important  part 
in  climatic  changes,  especially  in  the  United  States,  as 
will  appear  from  the  chapter  on  "  Cold  Waves." 

Repeated  and  careful  experiments  have  conclusively 
shown  that  radiation  proceeds  at  its  maximum  rate  to 
the  clear  sky.  It  is  further  intensified  by  the  absence 
of  aqueous  vapor  from  the  air,  and  is  diminished 
whenever  clouds  or  any  intervening  object  cuts  off  the 
clear  heavens. 


42  AMERICAN   WEATHER. 

Terrestrial  radiation  is  commonly  measured  by  a 
minimum  thermometer,  usually  black  bulb,  which  is 
exposed  at  the  height  of  the  grass,  on  green  sward. 
Clay,  gravel,  or  earth  are  poor  radiators,  while  grass 
and  kindred  vegetation  radiate  heat  much  more  rap- 
idly. The  lamp-black,  covering  the  thermometer  bulb, 
is  used,  owing  to  its  having  the  greatest  radiating 
power  of  any  known  substance. 

The  only  extensive  and  regular  set  of  observations 
on  nocturnal  radiation  are  those  which  have  been  car- 
ried on  for  a  number  of  years  in  India.  As  a  general 
rule,  the  greatest  difference  between  the  temperature  of 
an  ordinary  minimum  thermometer  and  of  the  black 
bulb  occur  in  the  winter  months,  when  average  dif- 
ferences of  from  12°  to  15°  are  not  unusual.  The  great- 
est average  monthly  difference  in  India  is  19°,  at  Chi- 
kalda,  in  December ;  the  greatest  difference,  for  a 
single  observation,  was  noted  at  Simla,  31°,  in  Decem- 
ber, 1884. 

An  equally  great  difference  between  the  minimum 
black  bulb  and  the  shade  minimum  was  observed  at 
Fort  Conger,  31°,  December  28th,  1882.  The  maximum 
difference  was  25°  at  both  Point  Barrow  and  Fort  Rea 
in  1882-83.  This  difference  depends  largely  on  the  still- 
ness of  the  air,  being  greatest  when  it  is  perfectly  calm. 

An  accurate  knowledge  of  the  conditions  under 
which  extreme  radiation  occurs  and  the  extent  to 
which  it  lowers  the  temperature  of  vegetation  or  other 
substances  is  not  alone  of  interest,  but  is  practically 
of  importance.  Experienced  gardeners  partly  avoid 
the  effects  of  late  and  early  frosts  by  planting  tender 
vegetation  on  hill-slopes  and  not  in  low-lying  lands, 
and,  when  clear,  calm  nights  follow  dry  winds  by  day, 
guard  against  radiation  and  protect  their  plants  by 
light  covering  of  straw,  etc. 


AMERICAN   WEATHER.  43 

In  Northern  India,  where  water  under  ordinary  con- 
ditions never  freezes,  advantage  was  taken  of  the  oper- 
ation of  Nature's  laws  to  obtain  a  supply  of  ice  by 
facilitating  radiation  and  evaporation. 

John  Eliot,  Esq.,  the  meteorological  reporter  to 
the  Government  of  India,  kindly  furnishes  to  the 
author  the  following  account  of  the  methods  followed 
in  India : 

"  This  method  was  formerly  practised  at  all  the 
large  stations  in  the  interior  of  Northern  India  (e.g., 
Umballa,  Lahore,  Meerut,  Agra,  Cawnpore,  Allahabad, 
Benares,  Patria,  and  as  far  east,  I  believe,  as  Hoogh- 

iy). 

"  At  Roorkee,  where  I  was  first  stationed,  the  follow- 
ing was  the  method  :  The  place  selected  was  open  and 
away  from  trees.  It  was  in  one  of  the  lowest  parts  of 
the  station,  with  rising  ground  in  all  directions  from  it ; 
shallow,  unclosed  porous  burnt-clay  dishes~~were  used 
of  elliptical  form,  and  were  placed  on  a  thick  bed 
of  straw  to  isolate  them  from  the  ground  as  far  as 
possible. 

"  The  period  during  which  ice  could  be  made  in  this 
way  lasted  from  November  to  February.  During  this 
period  perhaps  one  night  out  of  three  would  be  favor- 
able. Ice  could  only  be  made  on  perfectly  clear,  calm 
nights.  The  thinnest  veil  of  cloud  or  air  motion  of 
winds  was  fatal  to  success. 

"  The  most  favorable  nights  were  those  which  suc- 
ceeded stormy,  snowy  weather  in  the  Himalayas,  when 
the  air  in  Northern  India  is  for  a  few  days  unusually 
cool  and  dry  and  remarkably  clear  and  free  from  cloud, 
dust,  etc. 

"  When  the  weather  was  judged  to  be  favorable,  some 
thousands  of  these  shallow  dishes  were  nearly  filled 
with  water  during  the  afternoon.  Usually  (i.e.,  if 


44  AMERICAN  WEATHER. 

conditions  continued  favorable)  the  water  was  found 
to  be  converted  into  ice  next  morning. 

1 '  The  cause  of  the  formation  of  ice  was  undoubtedly 
the  rapid  radiation  which  takes  place  in  clear,  still 
nights,  during  the  cold  weather  in  Northern  India. 

"  This  effect  was  increased,  1st :  By  the  use  of  porous 
vessels.  The  outside  surface  evaporation,  due  to  slow 
percolation  of  water  through  the  sides  of  the  vessels, 
subtracted  heat  from  the  water  in  the  vessels.  2d : 
By  placing  the  vessels  on  straw,  thus  preventing  any 
flow  of  heat  from  the  earth  to  the  vessels." 


CHAPTER  V. 

HUMIDITY  AKD   EVAPORATION 

NOT  only  is  aqueous  vapor  an  abundant  element  of 
the  atmosphere,  but  it  is  meteorologically  most  im- 
portant, whether  in  gaseous,  liquid,  or  solid  form. 
Notwithstanding  the  great  stress  and  weight  meteorol- 
ogists place,  and  properly  so,  it  is  believed,  on  the 
intricate  relation  of  aqueous  vapor  to  the  development, 
progress,  and  intensity  of  storms,  yet  it  is  practically 
the  least  accurately  determined  and  most  unsatisfac- 
torily recorded  of  all  weather  elements. 

As  has  been  stated,  air  acts  according  to  a  certain 
law  in  altering  its  volume  under  changes  of  pressure 
and  temperature,  but  when  vapor  laden  there  are  cer- 
tain limits  to  the  gaseous  state.  A  cubic  foot  of  air, 
for  instance,  can  only  contain  aqueous  vapor  in  varying 
quantities,  dependent  almost  entirely  on  tempera- 
ture. When  the  limit  is  reached  the  air  is  said  to  be 
saturated,  and  if  the  temperature  is  lowered  it  follows 
that  some  of  the  aqueous  vapor  will  be  condensed  and 
pass  into  a  liquid  form,  as  dew  or  rain,  or  solid  form, 
as  snow,  hoar-frost,  etc. 

Before  this  limit  is  reached  the  air  will  absorb  moist- 
ure from  water  or  other  damper  surfaces  than  itself, 
as  from  snow,  ice,  etc.,  through  the  process  of  evapo- 
ration, whereby  the  snow  or  water  passes  rapidly  and 
most  often  invisibly  from  a  solid  or  liquid  to  the  gas- 
eous state.  Conversely,  by  the  process  of  condensation, 
owing  to  the  lowering  of  the  temperature,  the  aqueous 


46  AMERICAN  WEATHER. 

vapor  changes  rapidly  from  its  gaseous  condition  to  a 
liquid  or  solid  state. 

Since  a  large  quantity  of  heat  (the  latent  heat  of 
evaporation)  is  required  to  change  the  solid  or  liquid 
form  of  water  into  the  gaseous  condition  of  aqueous 
vapor,  it  follows  that  evaporation  lowers  the  temper- 
ature of  surrounding  bodies  from  which  the  heat, 
necessary  for  the  process,  is  drawn.  It  is  through  the 
effect  of  evaporation  that  perspiring  persons  are  cooled 
by  fanning  themselves  or  sitting  in  a  draught  of  air, 
and  by  similar  action  water  in  tropical  or  semi-tropical 
regions  is  kept  cool  either  by  the  evaporation  from 
the  exterior  surfaces  of  porous  vessels  or  from  wet 
cloth  coverings.  The  loss  of  heat  thereby  from  any 
given  surface  is  directly  proportional  to  the  absolute 
quantity  of  water  evaporated  from  it. 

High  temperature  and  strong  winds  favor  evapora- 
tion greatly,  since  at  high  temperatures  not  only  will 
the  air  contain  more  vapor,  but  the  water  passes  more 
quickly  into  the  gaseous  stage ;  and  the  greater  the 
quantity  of  air  comparatively  free  from  vapor  pass- 
ing over  the  water  surface,  so  much  the  more  is  evap- 
oration facilitated.  Evaporometers  (or  atmometers)  in 
general  use  are  of  two  classes,  the  first  of  which  deter- 
mines the  evaporation  by  the  use  of  a  balance,  whereby 
the  loss  of  weight  is  measured.  This  class  is  indis- 
pensable in  satisfactorily  determining  evaporation 
from  earth,  soils,  etc.,  in  agricultural  experiments. 
The  second  class  measures  the  changes  of  level  in  free 
water  surfaces,  the  pipe  in  which  the  measurements 
are  made  being  often  much  smaller  than  the  exposed 
pan  from  which  it  is  fed,  so  that  even  slight  evapora- 
tion is  quite  accurately  measured. 

Mitchell's  and  Von  Lamont's  are  evaporometers  of 
the  second  class,  which,  however,  is  giving  way  to  a 


AMERICAN  WEATHER. 


47 


third  form,  wherein  the  evaporation  is  not  from  a  free 
surface  of  water,  but  from  a  moistened  porous  bulb  or 
paper  disk,  which  allows  water  to  slowly  escape  from 
a  glass  tube. 

The  Piche  evaporometer,  Fig.  8,  consists  of  clean 
or  distilled  water  in  a  glass  tube,  nine  inches  in  length, 
which  is  graduated  to  show  the  contents 
in  cubic  centimetres  and  in  tenths. 
Evaporation  takes  place  from  the  sur- 
face of  a  paper  disk,  which  is  kept  in 
place  at  the  lower  open  end  of  the  tube 
by  a  brass  spring  attached  to  a  slitted 
collar  that  moves  along  the  tube.  Evap- 
oration is  about  twice  that  from  an  equal 
surface  of  free  water,  as  shown  by  the 
observations  of  Foerster  and  Biegler, 
but  the  rate  varies  with  different  ex- 
posed areas,  and  must  be  determined  for 
each  class  of  instruments.  These  evap- 
orometers  are  used  at  special  stations 
of  the  Signal  Service,  in  order  to  ascer- 
tain the  relation  between  the  amount 
of  evaporation  and  the  mean  daily 
temperature  and  dew-point,  and  the 
wind  velocity.  The  instrument  is  sus- 
pended in  the  shade,  and  the  tube  is 
refilled  as  often  as  is  necessary,  the 
paper  disks  being  renewed  at  the  same 
time.  The  instrument  cannot  be  used 
in  temperatures  below  32°. 

Observations  on  evaporation  have  been  quite  un- 
satisfactory, owing  to  the  rate  varying  with  dis- 
similar surfaces,  whether  of  shape  or  substance ;  to 
the  fact  that  the  vapor  diffuses  itself  irregularly, 
and  because  methods  of  exposure  and  measurement 


FIG.  8.— PICHE 
EVAPOROMETER. 


48  AMEKICAK   WEATHEK. 

have  not  been  such,  as  to  make  the  observations  com- 
parable. 

The  outcome  of  scattered  observations  is  the  general 
expression  that  the  annual  evaporation  from  free  water 
surfaces  near  the  ocean  substantially  agrees  with  the 
yearly  rainfall.  Among  amount  recorded  may  be 
noted  Madras,  92.2  inches  ;  Nagpur,  73.2  ;  London, 
20.6  ;  Fort  Conger,  81°  44'  K,  64°  45'  W.,  8.9.  In 
connection  with  the  observations  from  the  latter  sta- 
tion, it  is  of  interest  to  note  that  its  evaporation,  as 
calculated  from  eight  months'  observations,  exceeded 
the  rainfall  nearly  five  inches  ;  also  that  evaporation 
from  ice  and  snow  ceased  for  a  period  of  four  and  a 
half  months,  with  a  mean  temperature  of  —  31°. 

The  amount  of  moisture  in  the  air  is  measured  by 
hygrometers.  There  are  in  quite  popular  use  a  num- 
ber of  instruments  called  hygroscopes,  which  indicate 
only  changes  of  humidity.  The  best  known  of  these 
is  the  toy  ;  a  woman  emerges  from  a  little  house  dur- 
ing dry  weather,  and  the  man  in  wet  weather.  The 
action  of  these  figures  depends  on  the  well-known 
principle  that  the  length  of  catgut,  whalebone,  or  the 
human  hair  varies  largely  through  change  of  moist- 
ure. 

Saussure  and  others  have  demonstrated  the  accuracy 
with  which  a  human  hair,  under  proper  conditions, 
will  indicate  the  relative  humidity  of  the  air.  Some 
hair  before  breaking  will  support  a  weight  of  nearly 
four  ounces,  and  will  stretch  nearly  one  third  its 
length.  The  elasticity  of  the  hair  is  easily  destroyed 
by  the  slightest  excess  of  weight  or  by  protracted  ten- 
sion near  its  limit  of  perfect  elasticity.  The  weight 
should  not  exceed  one  half  gramme,  which  applied  to 
a  thoroughly  damp  hair  keeps  it  straight. 

Many  patterns  of  hair  hygrometers  have  been  de- 


show  Ike  nwr&er  of 
of  wetter  2o  each,  ci&iafoalqfa.in 


AMERICAN   WEATHEK. 


49 


vised,  in  order  to  obviate  the  well-known  errors  inci- 
dent to  observations  of  humidity  deduced  from  read- 
ings of  the  dry  and  wet  thermometers  at  temperatures 
below  the  melting  point  of  ice. 

The  Koppe  hair  hygrometer  is  largely  used  in  Europe, 
and  while  not  perfect,  is,  perhaps,  the  best.  The  hair 
(see  Fig.  9),  fastened  to  a  spring  loaded  with  a  half 
gramme  weight,  is  wound  around 
the  axle  of  a  dial  needle.  The 
adjustment,  made  by  experiment 
or  comparison,  is  such  that  in  a 
wholly  saturated  atmosphere  the 
needle  stands  at  100  on  a  scale 
graduated  from  0,  total  dryness, 
to  100,  complete  saturation.  The 
scale  readings  give  the  relative 
humidity  in  percentages,  but  the 
absolute  humidity  in  grains  of 
aqueous  vapor  to  a  cubic  foot  of 
air,  or  the  dew-point  of  the  air 
can  be  obtained  by  computation, 
for  which  an  additional  observa- 
tion of  the  dry  thermometer,  sus- 
pended in  the  case,  is  necessary. 

Professor  Harkness  has  devised  a  convenient  and 
reliable  form,  where  the  hair,  suspended  in  a  small 
metal  tube,  is  weighted  by  one  fifth  of  a  gramme.  A 
micrometer  screw  and  scale  permit  the  easy  determina- 
tion of  the  elongation  of  this  hair.  The  values  of  the 
scale  readings,  which  though  arbitrary  are  constant 
under  similar  hygrometrical  conditions,  are  determined 
by  comparative  simultaneous  observations  with  Reg- 
nault's  apparatus  or  from  dry  and  wet  thermometer 
readings.  This  instrument  is  compact,  simple,  and 
reliable  ;  it  is  worthy  of  careful  test  and  examination. 


FIG.  9.— KOPPE'S  HAIR 
HYGROMETER. 


50 


AMERICAN  WEATHER. 


The  most  accurate  method  of  measuring  the  humid- 
ity is  by  direct  hygrometers,  such  as  Daniell's  or  Reg- 
nault's,  which  are  constructed  on  the  principle  of  con- 
densation through  evaporation. 

Eegnault's  hygrometer,  Fig.  10,  consists  of  two 
cylinders,  the  lower  ends  of  which,  D  D,  are  of  highly 


FIG.  10. — REGNAULT'S  HYGROMETER. 

polished  silver,  while  the  upper  parts  are  of  glass. 
Two  thermometers,  T  T,  inserted  in  the  top,  have  their 
bulb  near  the  silver  bottom,  one  cylinder  being  empty 
and  the  other  partly  filled  with  ether,  so  as  to  cover 
the  bulb  of  the  thermometer.  An  aspirator,  A,  con- 
nected with  the  base  of  the  hollow  upright  and  cross- 
arms,  Y  U,  draws  nearly  equal  quantities  of  air  by 
each  thermometer.  One  thermometer  thus  acquires 
the  temperature  of  the  external  air.  The  other,  chilled 
by  cold  from  the  evaporation  of  ether,  caused  by  the 
air  drawn  through  it  from  the  tube  t,  falls  to  the 
dew-point,  which  is  indicated  by  the  appearance  of  a 
thin  film  of  dew  on  the  polished  silver.  The  reading 
of  this  thermometer  when  dew  forms  gives  the  tem- 


AMERICAN   WEATHER.  51 

perature  of  the  dew-point.  The  apparatus  and  its 
manipulation  are  costly  and  inconvenient,  so  that  the 
instrument  is  used  only  in  important  and  accurate 
experiments,  or  in  order  to  test  or  graduate  the  indica- 
tions of  other  simpler  and  less  expensive  hygrometers. 

The  relative  humidity  is,  however,  obtained  most 
commonly  in  the  United  States  from  simultaneous 
readings  of  the  dry  and  wet  thermometers,  exposed 
side  by  side,  as  shown  in  Fig.  6.  The  cold  of  evap- 
oration causes  the  wet  bulb  to  read  lower  than  the  dry, 
unless,  as  rarely  occurs,  the  air  is  completely  satu- 
rated. The  wet  thermometer  does  not  give  the  temper- 
ature of  the  dew-point,  but  it  sinks  to  a  point  between 
it  and  the  temperature  of  the  air  shown  by  the  dry 
thermometer.  The  difference  between  the  readings  of 
the  dry  and  wet  thermometers  bears  a  certain  and 
quite  constant  ratio  to  the  complement*  ol. the  dew- 
point,  so  that  by  an  empirical  formula  the  dew-point 
can  be  determined.  In  order  to  avoid  the  labor  of  cal- 
culation, tables  have  been  elaborated,  based  usually  on 
the  factors  formulated  by  Sir  James  Glashier,  F.R.S., 
having  been  empirically  obtained  from  the  comparison 
of  a  very  large  number  of  simultaneous  observations 
with  Daniell'  s  hygrometer  and  the  dry  and  wet  ther- 
mometers. 

From  these  readings,  then,  can  be  obtained,  first, 
the  dew-point ;  second,  the  elastic  force  of  vapor  (that 
is,  the  amount  of  barometric  pressure  due  to  aqueous 
vapor  present  in  the  air)  ;  third,  the  quantity  of  vapor 
in  each  cubic  foot  of  air.  These  values  are  to  be  found 
in  Table  No.  5. 

An  examination  of  the  table  shows  that  the  tension 


*  This  complement  is  the  difference  between  the  dew-point  and  the  tem- 
perature of  the  air. 


52  AMERICAN  WEATHER. 

of  saturation  decreases  with  greater  proportional 
rapidity  than  does  the  temperature,  a  diminution  of 
one  half  the  amount  at  80°  taking  place  in  a  fall  of 
21°,  while  at  20°  a  similar  decrease  occurs  with  a  fall 
of  15°.  This  important  fact  tends  to  facilitate  the  for- 
mation of  clouds.  For  instance,  the  mixing  of  equal 
masses  of  dry  air  results  in  a  temperature  the  mean  of 
the  two,  but  the  resulting  tension  of  saturation  is  al- 
ways less  than  the  mean  of  the  original  tensions.  For 
example,  the  tension  of  saturation  at  70°  is  equal  to 
.733  inch  of  mercury,  but  the  tension  of  saturation  at 
80°  is  1.023  inch,  and  at  60°,  .518,  the  mean  of  which 
is  .770,  so  that,  except  a  small  quantity  kept  in  the 
gaseous  state  by  the  emission  of  heat  from  the  conden- 
sation, an  amount  of  vapor  exerting  a  pressure  of  .037 
inch  must  be  condensed. 

The  distribution  of  aqueous  vapor  is  but  imperfectly 
known  and  locally  determined,  so  that  the  process  of 
obtaining  the  pressure  of  dry  air  by  deducting  the 
actual  tension  of  vapor,  while  the  best  method,  must  be 
considered  as  only  approximately  correct. 


I  figures  3%oH>  ike  number  qf 


of  rater  fa  tack  cu&icfealofair. 


( •  J  &  *  w « 

V^.4  -  ,%&$% 


CHAPTER  VI. 

AND   HOW   MEASURED. 

THE  apparent  capriciousness  of  wind  has  given  rise 
to  many  proverbs  as  to  its  variableness,  and  until  re- 
cent advances  in  meteorology  no  one  questioned  the 
truth  of  the  saying :  "  The  wind  bloweth  when  it 
listeth,  and  thou  canst  not  tell  whence  it  cometh 
and  whither  it  goeth."  Observations  and  research 
show,  however,  that  winds  are  subject  to  definite 
laws. 

The  direction  of  the  wind  is  designated  by  the  point 
from  which  it  blows,  as  north,  north -by-east,  etc.  In 
general,  the  wind  is  recorded  to  the  eight  principal 
points  of  the  compass,  but  in  more  exact  observations 
it  is  recorded  in  degrees  of  azimuth,  as  N.  10°  E.  or 
ten  degrees  east  of  North.  In  determining  the  point 
from  which  the  wind  is  blowing,  great  care  must  be 
taken  to  use  true  bearings  only.  If  this  is  not  done 
the  error  may  sometimes  be  a  serious  one,  since  the 
wind  blowing  from  the  same  direction  might  be  re- 
corded at  Eastport,  Me.,  by  compass  bearings  as  north- 
west, and  at  Olympia,  Wash.  Terr.,  as  north.  This 
results  from  the  well-known  fact  that  the  magnetic 
needle  points  absolutely  to  the  North  Pole  only  in  a 
few  places,  and  that  elsewhere  it  has  a  variation  either 
to  the  east  or  the  west  of  the  true  north.  In  Table 
No.  6  will  be  found  the  present  magnetic  variations 
at  principal  points  in  the  United  States. 

The  wind- vane  should  rise  above  all  surrounding 


54  AMERICAN   WEATHEK. 

buildings  or  objects,  so  that  the  wind  may  act  freely 
upon  it.  The  vane  itself  should  be  long  and  light 
enough  to  be  easily  moved,  its  support  exactly  per- 
pendicular, and  its  bearing  kept  well  oiled.  The  vane 
should  balance  on  its  support,  and  its  tail  should  pre- 
sent a  much  larger  amount  of  surface  than  its  head, 
since  the  directive  tendency  depends  upon  the  differ- 
ence of  the  wind's  action  upon  the  head  and  tail. 

Yarious  devices  have  been  used  for  registering  the 
direction  of  the  wind.  Draper,  Beck,  Wild,  Osier,  and 
others  have  invented  methods  quite  as  ingenious  but 
more  complicated  than  the  simply  mechanical  appa- 
ratus of  Eccard.  In  this  case  the  prolongation  of  the 
vane  through  the  roof  terminates  at  its  lower  end  in  a 
toothed  wheel,  which  is  geared  into  a  second.  The 
latter  wheel  is  at  the  top  of  an  endless  screw,  which 
moves  up  or  down  as  the  vane  swings  to  and  fro,  a 
pencil  pressing  constantly  against  and  recording  on  a 
paper-covered  drum  turned  by  clockwork  once  each 
day.  The  only  defect  arises  from  the  records  of  calm 
and  light  steady  winds  being  undistinguishable. 

The  most  satisfactory  record  is  that  obtained  from  a 
modification  of  Gibbons' s  electrical  self -registering 
anemometer.  By  increasing  the  number  of  magnetic 
circuits  to  four  and  enlarging  the  drum  (see  Fig.  11)  as 
each  mile  of  wind  is  recorded,  its  direction  is  also  in- 
dicated either  by  letter,  as  N.,  KE.,  etc.,  or  by  a  dot 
or  mark  on  the  corresponding  direction  lines. 

Of  even  greater  importance  than  the  direction  of  the 
wind  is  its  force,  which  may  be  measured  directly  by 
its  pressure  or  its  velocity  by  instruments  called  ane- 
mometers. The  oldest  method  of  observing  the  force 
of  the  wind  is  by  estimation,  a  somewhat  rough  but 
necessary  mode  in  the  absence  of  modern  instrumental 
appliances.  The  scale  devised  by  Sir  Francis  Beaufort 


AMERICAN  WEATHER. 


56  AMERICAN  WEATHER. 

is  in  quite  general  use,  running  from  1,  light  air,  to  12, 
hurricane.  Other  arbitrary  scales,  from  1  to  4,  1  to  6, 
1  to  8,  and  1  to  10,  cover  the  same  range  as  does  the 
Beaufort  scale.  The  conversion  of  these  arbitrary 
scales  to  miles  of  velocity  or  pounds  of  pressure  is 
quite  impracticable,  but  the  words  light  air,  gentle 
wind,  strong  breeze,  gale,  and  hurricane  convey  more 
exact  ideas  and  are  more  satisfactory  than  the  above 
scales.  Fortunately,  simple  and  fairly  exact  instru- 
ments for  determining  the  velocity  of  the  wind  are  not 
uncommon. 

The  wind  gauge  devised  by  Lind  measures  the  press- 
ure by  the  displacement  of  water  in  a  siphon,  one  end 
of  which,  bent  at  right  angles,  faces  the  wind.  The 
siphon  turns  freely  on  a  vertical  axis,  and  a  vane  keeps 
its  mouth  to  the  wind  ;  the  instrument  is  now  rarely 
used.  A  more  satisfactory  method  is  that  of  measur- 
ing the  pressure  of  the  wind  on  a  plane  surface  per- 
pendicular to  the  wind's  direction.*  The  plate,  kept 
perpendicular  to  the  wind  by  a  vane,  when  moved  by 
the  wind  acts  on  a  spring  or  lever,  by  means  of  which 
the  degree  of  pressure  is  measured.  Sometimes  a 
swinging  plate  is  suspended  by  its  horizontal  edge, 
with  its  lower  edge  free  to  remain  perpendicular  or  to 
be  inclined  at  an  angle  corresponding  to  the  force  of 
the  wind.  Professor  Wild's  pressure  gauge  is  of  this 
form,  which  the  Vienna  Meteorological  Congress  rec- 
ommended. Osier  and  Gator,  in  England,  and  Draper, 
in  America,  have  devised  quite  reliable  instruments  on 


*  Colonel  James  devised  a  convenient  rule  by  which  pressure  can  be 
converted  quite  accurately  to  velocity,  by  multiplying  the  pounds  of  press- 
ure per  square  foot  by  200,  and  extracting  the  square  root  of  the  product, 
which  gives  the  miles  per  hour.  Conversely,  the  square  of  the  velocity 
in  miles  per  hour  multiplied  by  .005  gives  the  pounds  of  pressure  to  each 
square  foot. 


AMERICAN"   WEATHER. 


57 


the  principle  of  pressure,  and  the  records  of  these  in- 
struments, made  by  violent  gusts,  are  most  satisfac- 
tory. Unfortunately,  they  cannot  be  considered  as 
absolutely  accurate,  since  readings  of  separate  instru- 
ments are  not  strictly  comparable,  as  different  instru- 
ments of  the  same  pattern,  with  the  same  size  of  plate, 
have  given  discordant  results.  It  is  also  well  known 
that  the  force  exercised  by  the  wind  upon  each  square 
foot  of  surface  depends  upon  the  size  and  form  of  the 
plate,  and,  perhaps,  upon  other  conditions. 

The  velocity  anemometer  which  most  generally  com- 
mends itself  is  that  devised  by  Dr.  Kobinson  (Fig.  12). 


FIG.  12. — ROBINSON'S  ANEMOMETEK. 


58  AMERICAN  WEATHEK. 

At  the  ends  of  two  horizontal  rods,  crossing  each  other 
at  right  angles,  are  fastened  four  hollow  hemispheres, 
with  their  open  surfaces  in  the  same  direction,  so  that 
they  may  receive  the  wdnd  freely.  These  cups  are  sup- 
ported on  a  vertical  rod,  which  is  so  mounted  with 
bearings  that  it  turns  freely  in  a  hollow  tube  and  sets 
in  motion  by  an  endless  screw  at  its  lower  end  a  set  of 
index  wheels. 

The  dials  of  the  index  wheels  are  so  arranged  that 
they  show  every  mile  of  wind  which  passes.  By  means 
of  an  electrical  device  invented  by  Lieutenant  Gibbon, 
United  States  Army  (see  Fig.  11),  each  mile  of  wind  is 
recorded  on  a  properly  ruled  blank  form,  which,  r£- 
volving  on  a  drum,  contains  the  record  for  a  day. 

The  anemometer  should  be  kept  in  a  vertical  posi- 
tion and  at  such  a  height  as  to  expose  it  to  the  full 
force  of  the  wind.  It  should  be  kept  free  from  dust 
and  dirt  and  be  carefully  oiled,  so  as  to  prevent  fric- 
tion and  injury  to  the  different  bearings,  and  the  dial 
screw,  while  kept  tight,  should  not  be  sufficiently  so 
to  interfere  with  the  free  motions  of  the  dials. 

The  gearing  of  the  dials  for  the  mileage  registration 
of  the  Robinson  anemometer  is  based  on  the  supposi- 
tion that  the  travel  of  the  wind  is  exactly  three  times 
the  distance  travelled  by  the  centre  of  the  cups.  This 
supposition  is  only  approximately  true,  as  experi- 
ments show  that  the  relation  between  the  wind  travel 
and  that  of  the  centre  of  the  cup  varies  from  2.3  to 
3.0,  depending  on  the  size  of  the  cups,  length  of  arms, 
and  the  wind  velocity.  For  the  smaller  anemometers, 
four-inch  cups  on  six-inch  arms,  the  relation  is  very 
nearly  3.0.  For  nine-inch  cups  on  twenty-four-inch 
arms,  the  Kew  pattern,  it  is  not  more  than  about  2.5. 
It  follows  that  wind  velocities  measured  with  the  lat- 
ter instruments,  which  are  always  geared  to  give  three 


AMERICAN  WEATHER.  59 

times  the  travel  of  cup,  must  be,  at  least,  twenty  per 
cent  too  high. 

The  ratio  between  wind  travel  and  cup  travel  dimin- 
ishes as  the  velocity  of  the  wind  increases.  While  3  may 
be  a  correct  ratio  for  an  instrument  when  the  wind  is 
four  miles  an  hour,  the  ratio  may  not  be  more  than  2.5 
for  winds  of  thirty  miles  an  hour. 

In  anemometers  having  short  arms  and  large  cups, 
the  ratio  for  all  velocities,  high  and  low,  is  more  nearly 
constant  than  in  the  case  of  long-armed  instruments, 
as  at  higher  velocities  the  cups  on  short  arms  shade 
each  other  in  parts  of  their  revolutions. 

Jt  is  especially  important  that  the  anemometer  should 
have  a  free,  open  exposure  at  such  an  elevation  as  to 
insure  the  instrument  receiving  the  full  force  of  the 
wind.  The  elevation  is  an  important  consideration, 
since  the  velocity  of  the  wind  increases  quite  regularly 
up  to  one  thousand  feet. 

The  average  daily  velocity  of  the  wind  is  obtained 
similarly  to  other  daily  means,  but,  as  a  rule,  the 
diurnal  variation  of  the  wind  is  so  great,  as  will  be 
seen  in  a  later  chapter,  that  its  interest  is  secondary 
to  that  of  the  means  of  the  hours  of  greatest  and  least 
velocity.  In  some  instances  over  half  the  wind  of  the 
day  blows  during  seven  or  eight  hours. 


CHAPTER  VII. 

PRECIPITATION— FOG,  CLOUD,  RAIN,  AND    SNOW. 

THE  precipitation  of  the  aqueous  vapor  of  the  air 
may  be  divided  into  two  general  conditions,  the  first  of 
which  obtains  when  the  vapor  is  visible  in  the  air,  oc- 
curring in  the  shape  of  mist,  fogs,  and  clouds  ;  or,  sec- 
ondly, when  it  reaches  the  surface  of  the  earth,  in  the 
form  of  dew,  hoar-frost,  rain,  snow,  sleet,  or  hail. 
Mists,  fogs,  and  clouds  are  of  the  same  general  class  ; 
the  cloud  differing  only  from  the  mist  or  fog  by  its 
height  and  the  changed  conditions  which  arise  from 
the  cold  of  elevation.  The  water  particles  which  make 
up  these  visible  forms  of  aqueous  vapor  are  of  a  minute 
size,  being  estimated  to  vary  from  .0006  to  .0050  inch 
in  diameter. 

It  was  formerly  advanced  that  these  minute  drops 
of  rain  or  fog  were  vesicular— that  is,  hollow  spheres  ; 
but  later  experiments  and  observations  go  to  show  that 
not  only  are  they  solid  bodies,  but  that  they  form 
around  some  minute  particle  of  dust  in  the  atmosphere. 

Fog  and  cloud  are  supported  in  the  air  partly  by  the 
upward  tendency  of  the  air  currents,  partly  by  the  re- 
sistance of  air  to  the  falling  of  minute  spherical  bodies, 
which  is  doubtless  increased  by  the  varying  density  of 
the  different  strata  of  air.  When  ascending  air  cur- 
rents cease,  the  particles  immediately  commence  to  fall 
by  their  own  weight,  and  frequently  in  so  doing  are 
again  converted  into  aqueous  vapor  by  passing  into  a 
stratum  of  air  of  a  higher  temperature,  which  is  not 


AMEKICAK   WEATHER.  61 

in  a  state  of  saturation.  These  phenomena  are  visible 
any  summer  day,  when  but  slight  observation  is  neces- 
sary to  note  the  continually  changing  shapes  and  forms 
of  the  clouds,  which  either  diminish  or  increase,  never 
remaining  uniform  and  stationary. 

Mists  and  fogs  are  generally  of  local  distribution,  and 
are  produced  by  two  methods  :  first,  by  warm,  very 
moist  winds  blowing  over  the  surface  of  cold  water,  and, 
second,  by  cold  winds  passing  over  very  warm  water 
or  damp,  moist  ground.  Consequently  fogs  occur  with 
the  greatest  frequency  in  those  regions,  on  or  near 
large  bodies  of  water,  where  great  differences  in  tem- 
perature are  found  in  comparatively  short  distances. 

Within  the  Arctic  circle  the  continued  presence  for 
the  months  of  the  summer  sun  is  not  marked  by  fair, 
bright  days,  but,  on  the  contrary,  fogs  are  almost  con- 
stantly present  over  the  sea,  and  the  sun  is  hidden  for 
many  successive  days.  Such  fogs  are  frequently  only 
150  to  200  feet  deep,  and  from  the  high  ground  near 
Fort  Conger  the  author,  from  1881-83,  rarely  saw  the 
adjacent  ice-filled  straits  free  for  any  prolonged  period 
from  low-lying  sheets  of  fog  and  mist.  In  winter  these 
vapors  overhung  the  ice-cracks  or  tide-holes,  but  in 
summer  they  were  quite  general,  except  in  windy 
weather.  Scoresby  notes  that  in  1817,  among  open  ice 
in  the  Greenland  Sea,  he  experienced  a  fog  which 
never  once  cleared  for  fifteen  days,  while  in  1821, 
from  July  llth  to  August  21st,  an  interval  of  forty- 
one  days,  three  days  only  were  free  from  fog. 

On  the  North  Pacific  coast  fogs  prevail  during  win- 
ter, and  their  advent,  coincident  with  the  rains,  marks 
the  beginning  of  the  rainy  season.  They  come  with 
quite  a  degree  of  regularity  at  New  Westminster, 
B.  C.,  about  the  middle  of  October.  These  fogs  in 
California  are  sometimes  over  1500  feet  thick,  and 


62  AMERICAN   WEATHER. 

their  advent  and  passage  over  the  interior  valleys  do 
not  a  little  to  relieve  the  aridity  of  the  country.  As 
much  as  .05  of  an  inch  of  water  in  depth  has  been  de- 
posited by  fog  in  a  single  night. 

Along  the  Atlantic  coast  fogs  are  most  prevalent 
from  the  New  England  coast  northeastward  to  New- 
foundland, increasing  in  density  and  frequency  as 
one  goes  northward.  It  has  long  been  known  that  the 
fog  conditions  upon  these  coasts  are  caused  by  the 
winds,  warmed  and  vapor-ladened  by  their  passage  over 
the  Gulf  Stream,  being  drawn  over  the  cold  surface 
current  which  flows  along  these  coasts.  Sergeant  Gar- 
riott,  of  the  Signal  Service,  has  lately  defined  more 
clearly  the  cause  of  these  fogs,  and  has  shown  that 
they  have  a  definite  relation  to  the  advance  and  passage 
of  low  area  storms  over  the  United  States  and  New- 
foundland. The  fog  is  found  only  in  the  east  and 
south  quadrants  of  these  storms,  so  that  its  coming 
and  passing  is  intimately  connected  with  the  storms 
themselves,  and  can  be  predicted  with  a  fair  degree  of 
certainty  several  days  in  advance. 

CLOUDS. 

The  numberless  forms  of  clouds  make  it  difiicult  to 
so  classify  and  name  them  as  to  secure  easy  recognition 
and  ensure  uniformity  of  record.  The  fair-weather, 
the  thunder  and  rain  clouds  are  such  forms  as  impress 
even  the  casual  observer,  and  give  very  definite  indica- 
tion of  the  coming  weather  ;  but  such  expressions  do 
not  convey  to  meteorologists  clear,  definite  ideas  as  to 
the  exact  shape,  definite  formation  or  approximate  ele- 
vation of  the  clouds  observed. 

The  necessity  of  an  exact,  comprehensive,  but  simple 
nomenclature  has  long  been  apparent,  but  despite  the 
efforts  of  several  distinguished  meteorologists,  partic- 


AMERICAN   WEATHER.  63 

ularly  Hildebrandsson  and  Ley,  all  attempts  to  reform 
and  extend  the  present  system  have  failed. 

The  present  classification,  of  three  simple  and  four 
compound  forms,  is  that  of  Luke  Howard,  and  has  re- 
mained unchanged  since  its  introduction  in  1803. 

The  cirrus,  always  of  great  elevation,  is  a  cloud  of 
fibrous  form,  and  is  characterized  by  its  great  variety 
in  shape,  a  marked  delicacy  of  substance,  and  its  sin- 
gularly pure  white  texture. 

The  cumulus,  of  moderately  low  elevation,  especially 
the  cloud  of  a  summer  day,  assumes  in  its  simpler 
form  the  shape  of  conical  heaps  rising  from  a  horizontal 
base.  It  may  be  seen  in  warm  afternoons  rising  with 
an  ascending  air  current  in  huge  masses,  meeting  and 
drifting  with  horizontal  currents.  When  these  clouds 
gradually  dissolve  they  indicate  fine  weather.  In  other 
cases  the  clouds  increase  in  size  and  extent,  while  the 
woolly  white  texture  of  the  cloud  gradually  assumes 
a  darkish  tint. 

The  stratus  is  the  lowest  of  all,  generally  gray  masses 
or  sheets  of  cloud  with  illy-defined  outlines. 

The  term  nimbus  is  applied  to  any  cloud  or  clouds 
from  which  rain  or  snow  is  falling. 

There  is  a  form  of  cloud  partaking  of  the  character- 
istics of  both  cirrus  and  cumulus,  which  is  called  the 
cirro-cumulus.  Its  most  striking  form,  small  round 
masses  of  cloud,  apparently  cirrus  bands  broken  and 
curled  up,  is  commonly  known  as  the  mackerel  sky. 

When  the  cirrus  arranges  itself  into  thin  horizontal 
layers,  it  is  called  cirro-stratus.  This  formation  is 
frequently  of  great  extent,  but  so  thin  perpendicularly 
that  the  sun's  rays  frequently  pass  quite  through  it. 

The  cumulo- stratus  is  the  cumulus  blended  with  the 
stratus.  Its  most  remarkable  form  is  in  connection 
with  approaching  thunder-storms,  often  called  thun- 


64  AMERICAN   WEATHER 

der-heads,  when  it  frequently  presents  a  magnificent 
spectacle  in  its  beautiful  form,  strong  contrasts  of 
light  and  shadow,  and  rapidly  changing  outlines. 

The  cirrus,  cirro-cumulus,  and  cirro-stratus,  named 
in  order  of  occurring  altitude,  are  known  as  upper 
clouds,  the  others  as  lower  clouds. 

Messrs.  Ekholm  and  Hagstrom  have  given  careful 
attention  to  the  elevation  of  the  various  kinds  of 
clouds,  and  from  over  1400  measurements  deduced  the 
following  conclusions  as  to  extreme  limits  of  elevation  : 

Mmbus,   from  3,700  feet  to    7,200  feet. 
Stratus,       "          600    "     "    3,500    " 
Cumulus,    "      4,900    "     "  14,000    " 
Cirrus,         "     18,000    "     "  22,400    " 

They  observed  that  clouds  have  strong  tendencies 
to  form  at  a  certain  definite  height,  and  were  most  com- 
mon at  elevations  of  about  5000  feet  and  at  22,000  feet. 

Observations  on  the  motions  of  upper  clouds  are  of 
great  importance,  since  from  these  movements  can  be 
gleaned  the  only  possible  information  as  to  the  prevail- 
ing direction  of  the  upper  air  currents.  This  knowl- 
edge is  valuable,  since  it  must  shed  light  on  general  at- 
mospheric currents,  and  also  may  lead  to  better  meth- 
ods of  weather  forecasts  in  which  abnormal  movements 
of  the  cirrus  clouds  may  be  an  important  factor. 

Cloudiness  is  usually  recorded  on  a  decimal  scale,  in 
which  0  indicates  clear  sky  and  10  complete  cloudiness. 
Fog  is  recorded  "  foggy"  when  spoken  of  as  weather 
by  the  United  States  Signal  Service,  but  in  estimating 
cloudiness,  it  is  recorded  as  zero  when  light  or  broken, 
but  if  it  envelops  everything  it  is  recorded  10. 

The  average  cloudiness  of  the  earth  is  probably  be- 
tween fifty  and  fifty-five  per  centum,  which  amount 
slightly  exceeds  the  cloud  conditions  of  the  United 


AMERICAN   WEATHER.  65 

States  to  the  east  of  the  Mississippi  River.  To  the 
westward  the  yearly  percentages  more  generally  range 
from  thirty  to  forty-five. 

In  the  Pacific  coast  and  Southern  Plateau  regions 
are  found  sharp  contrasts,  and  decided  departures  from 
the  mean  percentages  elsewhere.  In  Western  Texas, 
New  Mexico,  Arizona,  and  California,  the  average  an- 
nual percentages  of  cloudiness  range  from  twenty  per 
cent  to  thirty  per  centum.  In  Southeastern  California 
and  the  Valley  of  the  Colorado  obtains  the  minimum 
amount  of  cloud  in  the  United  States,  the  percentages 
being  only  nineteen  for  Keeler,  CaL,  and  seventeen  for 
Yuma,  Ariz.  Along  the  Pacific  coast  to  the  northward 
of  California,  however,  the  percentages  increase  very 
rapidly  ;  being  sixty-two  at  -Olympia  and  Tatoosh 
Island,  and  probably  the  increase  is  constant  north- 
ward to  Alaska,  since  at  St.  Michael's  the  percentage 
is  sixty-seven,  and  at  Unalaska  rises  to  the  extraordi- 
nary figure  of  eighty-two. 

Eastward  of  the  Mississippi  River  the  largest  per- 
centages of  cloudiness  are  found  on  the  shores  of  Lake 
Ontario,  ranging  from  sixty  at  Buffalo  to  sixty-three 
at  Oswego. 

The  monthly  fluctuations  of  cloudiness  are  of  greater 
importance  than  the  mean  cloudiness  for  the  year. 

Over  the  greater  part  of  the  area  of  the  United  States 
the  minimum  amount  of  cloudiness  for  a  month  occurs 
during  August,  and  in  consequence  the  cloudiness  of 
that  month  has  been  charted,  No.  XVIL,  as  one  of  the 
representative  months  of  the  extremes.  Over  a  small 
portion  of  the  upper  lake  region  July  has  a  slightly 
less  quantity  of  clouds  than  August ;  while  in  the  At- 
lantic States,  from  New  Jersey  to  Northern  Florida, 
the  least  clouds  are  observed  during  October. 

The  maximum  amount  of  mean  cloudiness  by  months 


66  AMERICAN  WEATHEE. 

is  illustrated  by  the  chart,  No.  XVL,  for  January, 
since  during  that  month  the  greatest  amount  of  cloudi- 
ness prevails  over  the  Pacific  coast  region  and  in  the 
South  Atlantic  and  Gulf  States.  From  New  England 
westward  to  Michigan  and  Illinois  the  cloudiness  is 
slightly  greater  during  December,  while  in  the  Mis- 
souri Valley  and  the  Rocky  Mountain  region  the  maxi- 
mum cloudiness  falls  during  the  months  of  March, 
April,  and  May. 

In  Fig.  13  is  shown  the  mean  cloudiness  for  the 
different  months  of  the  year,  deduced  from  many  years' 
observations  at  certain  stations  in  the  United  States. 
As  might  be  expected,  the  cloudiness  as  a  rule  is  much 
more  prevalent  in  winter  than  in  summer.  There  are 
notable  exceptions  to  this  rule,  which  show  that  local- 
ity has  much  to  do  with  the  shape  of  the  curves.  It 
will  be  noticed  that  the  curves  at  San  Francisco  and 
Yuma  are  in  general  accord,  with  a  marked  increase  of 
cloudiness  during  July  and  August ;  but  at  Olympia 
and  Sacramento,  both  in  the  Pacific  coast  region,  the 
shape  of  the  curves,  with  the  minimum  in  July  and 
August,  are  more  in  accord  with  those  for  the  rest  of 
the  country. 

The  most  striking  case  of  extreme  cloudiness  is  that 
at  Unalaska,  where  the  sky  was  almost  entirely  covered 
in  February,  1880,  there  being  but  three  per  cent  of 
clear  sky  during  the  month.  In  many  other  separate 
months  the  cloudiness  of  this  station  has  ranged  from 
ninety -one  to  ninety-three  per  centum. 

In  certain  localities  in  the  western  part  of  the  United 
States,  the  sky  is  almost  cloudless  in  certain  months  of 
the  year.  At  Yuma  the  percentage  of  cloudiness  for 
June  and  September  is  but  nine,  and  in  some  years 
during  these  months  the  percentage  has  been  as  low 
as  one.  The  months  of  June  to  September  are  al- 


tfean  Cloudiness 

for 

Januaiy 

\Signal  Service  Observations 

mn-4886 


UUI7BRSI7-: 


AMERICAN  WEATHER. 


67 


Animal  Fluctuations  of  Cloudiness. 


Stations' 


VewYorf 


Yrsirrsr 


1 1 


3 


70 


60 


40 


30 


20 


10 


i 


FIG.  13. 


most  cloudless  both  at  Keeler  and  Sacramento,  Cal., 
where  the  percentages  range  between  four  and  nine. 

The  total  absence  of  rain  and  the  practical  absence 
of  clouds  for  months  at  a  time  was  formerly  considered 


68  AMERICAN   WEATHER. 

to  make  this  section  of  the  country  practically  worth- 
less ;  but  of  late  years  it  has  proved  of  great  advantage 
for  an  important  industry  of  Southeastern  California, 
where  this  exceptionally  sunshiny  weather  permits  the 
curing  of  raisins  without  artificial  means. 

Little  attention  has  been  paid  to  the  diurnal  varia- 
tion of  cloud,  but  according  to  Buchan  a  maximum, 
more  pronounced  over  the  ocean  than  on  land,  occurs 
about  sunrise.  The  minimum  is  about  mid-day,  fol- 
lowed by  an  afternoon  maximum,  which  falls  by  mid- 
night to  a  secondary  minimum. 

DEW. 

The  phenomenon  of  dew  was  involved  in  mystery 
until  1814,  when  an  American,  Dr.  W.  C.  Wells,  then 
residing  in  England,  by  his  ingenious  and  careful  ex- 
periments discovered  the  conditions  under  which  dew 
forms.  Dr.  Wells  propounded  a  ''Theory  of  Dew" 
which  fully  explained  the  phenomenon,  and  which  is 
accepted  as  final. 

To  inhabitants  of  great  cities  the  most  familiar  form 
of  dew  is  that  which  gathers  in  the  shape  of  tiny  drops 
on  the  outside  of  glasses  and  other  vessels  containing 
cold  water,  when  they  are  exposed  in  a  close,  compara- 
tively warm  room,  when  the  air  is  moist.  This  process 
is  vulgarly  called  "sweating"  by  many  uninformed 
people,  who  believe  that  the  water  exudes  through  the 
sides  of  the  vessel.  It  is,  however,  only  an  illustration 
of  the  formation  of  dew,  the  warm,  moist  air  being 
chilled,  by  contact  with  the  cold  sides  of  the-  vessel,  be- 
low the  dew-point — i.e.,  acquiring  such  a  low  tempera- 
ture that  it  can  no  longer  hold  its  moisture  as  aqueous 
vapor,  and  so  deposits  it  on  the  cool  surface  as  dew. 
If  the  air  in  the  room  is  very  dry  no  dew  is  formed,  no 
drops  appear. 


AMERICAN   WEATHER.  69 

The  same  process  as  is  here  described  takes  place 
every  clear  calm  night  over  the  greater  part  of  the  land 
surfaces  of  the  earth.  The  chapter  on  radiation  sets 
forth  the  method  in  which  the  earth' s  heat  escapes  into 
space.  When  the  relative  humidity  of  the  air  is  high 
it  requires  but  slight  loss  of  heat  to  reduce  the  tempera- 
ture of  the  air  below  the  dew-point.  Such  action  takes 
place  with  the  greatest  rapidity  over  grasses  and  simi- 
lar vegetation  which  radiate  heat  rapidly,  and  the 
process  is  facilitated  by  light  air  coming  from  humid 
quarters,  whereby  the  air  which  has  given  up  part  of 
its  moisture  is  speedily  replaced.  The  economy  of 
nature  is  thus  shown  in  the  formation  of  dew,  as  in 
other  physical  laws,  since  the  enormous  radiating 
powers  of  vegetable  substances,  which  most  need  mois- 
ture for  growth  and  development,  ensure  their  receiv- 
ing the  greatest  possible  amount  of  dew. 

The  formation  of  dew  is  retarded  by  any  condition 
which  obstructs  radiation,  such  as  a  covered  or  partly 
shaded  sky,  whether  by  cloud,  foliage,  or  other  inter- 
vening object,  or  by  the  presence  of  wind  when  the 
constantly  moving  and  mixing  air  does  not  remain  in 
contact  with  the  cold  surfaces  long  enough  to  be  chilled 
below  the  dew-point. 

Dews  are  the  heaviest  in  low  latitudes  and  along 
coasts  where  the  prevailing  night  breeze  is  from  the 
sea,  since  the  air  passing  over  the  earth  is  then  not 
only  vapor-laden  to  such  an  extent  that  the  temperature 
of » the  dew-point  is  nearly  the  same  as  that  of  the  air, 
but,  from  its  high  temperature,  the  air  contains  a  large 
amount  of  aqueous  vapor. 

The  amount  of  dew  which  falls  varies  nightly  from 
zero  to  perhaps  .02  inch  according  to  local  conditions. 
But  few  systematic  observations  have  been  made 
with  a  view  to  determining  the  exact  amount,  which 


70  AMEEIC AN   WEATHER. 

has  been  estimated  for  the  British  Isles  to  be  not  far 
from  an  inch  and  a  half  for  the  year. 

The  dews  along  the  California  coast  occur  under  fa- 
vorable conditions  of  clear  sky,  with  light  airs  from  the 
ocean,  and  so  are  unusually  heavy — a  fortunate  cir- 
cumstance, which  materially  ameliorates  the  effects  of 
the  almost  rainless  summer. 

When  the  dew-point  of  the  air  is  at  a  temperature 
below  the  freezing-point,  the  moisture  then  condensed 
is  deposited  on  the  colder  radiating  surfaces  in  a  solid 
form,  as  Tioar-frost. 

KAINFALL. 

Rainfall  is  the  most  indefinite  of  the  various  mete- 
orological phenomena,  as  to  its  locality,  distribution, 
seasonal  recurrence,  and  amount.  It  is  impossible  to 
draw  a  sharp  line  between  mist  and  rain.  Whenever 
condensation  of  aqueous  vapor  takes  place  rapidly  and 
the  small  particles  of  mist  increase  in  diameter  it  is 
then  called  rain.  The  exact  manner  in  which  rain 
forms  is  not  known.  Different  theories  have  been  ad- 
vanced, some  assuming  that  two  masses  of  saturated 
air  of  different  temperatures  are  suddenly  combined, 
with  the  result  of  immediately  condensing  the  excess 
of  moisture  which  necessarily  results.  Others  urge 
that  rainfall  usually  occurs  by  the  cold  of  expansion 
or  elevation,  owing  to  large  masses  of  saturated  air  be- 
ing forced  upward  by  under-running  currents  of  cold 
air,  or  by  violent  out-draughts  of  warm  air  from  the 
upper  strata  of  the  atmosphere,  which  naturally  draw 
upward  the  saturated  air.  Doubtless  both  methods 
obtain  to  a  greater  or  less  extent,  and  it  is  susceptible 
of  proof  that  the  heaviest  rains  of  the  world  are  caused 
by  the  cold  of  expansion,  where  the  general  movements 
of  the  atmosphere  result  in  warm  moist  air  being  forced 
or  drawn  up  to  great  elevations  by  the  presence  of  ab- 


AMERICAN   WEATHER.  71 

rupt  mountain  ranges,  over  which  the  air  must  pass  and 
in  so  doing  lose  the  greater  part  of  its  vapor.  The  au- 
thor believes  in  the  general  law  advanced  by  Blanf  ord, 
that  "  however  vapor-ladened  may  be  any  current  of 
air,  however  saturated,  it  does  not  bring  rainfall  so 
long  as  it  preserves  a  horizontal  movement."  Either 
increased  elevation,  or  eddies  from  increase  of  friction, 
or  the  convection  around  borders  of  a  barometric  de- 
pression causes  formation  of  cloud  and  rain. 

Excessive  rainfall  on  land  occurs  at  places  in  middle 
or  lower  latitudes  contiguous  to  a  sea  of  comparatively 
high  mean  temperature  and  from  which  the  prevailing 
winds  blow.  The  heavy  rain  results  from  the  conden- 
sation of  moisture  by  cold,  caused,  as  some  suggest, 
partly  by  the  winds  passing  over  a  land  of  lower  tem- 
perature, or,  as  is  more  probable,  by  being  forced  up- 
ward, more  or  less  sharply,  by  the  configuration  of  the 
country. 

The  author,  from  a  somewhat  extensive  observation 
of  weather  conditions,  fails  to  find  any  cases  where 
the  vapor-ladened  air  is  apparently  cooled  to  any  extent 
by  radiation  or  convection  from  land  of  low  tempera- 
ture. The  process  of  cooling  a  body  of  moist  air  by 
its  own  radiation  into  space,  or  by  convection  or  radia- 
tion from  cold  land,  must  be  very  slow,  and  the  final 
effect  inconsiderable  ;  especially  as  compared  with  the 
cold  of  elevation,  which  is  about  half  a  degree  for  every 
hundred  feet  of  ascent. 

Deficient  rainfall  over  land  occurs  in  high  latitudes, 
where  the  mean  temperature  of  sea  and  air  are  both 
low.  In  low  latitudes  it  results  from  the  prevalent 
winds  having  been  deprived  of  the  greater  part  of  their 
moisture  by  having  passed  over  mountain  ranges  of 
considerable  elevation,  or  by  their  passing  over  a  coun- 
try having  nearly  the  same  temperature  as  the  region 


72  AMERICAN   WEATHER. 

from  which  the  moisture  was  drawn,  and  where  the 
country  does  not  rise  with  marked  abruptness.  Tran- 
quil atmospheric  conditions  arising  from  the  absence 
of  low  areas,  or  exemption  from  their  influence  owing 
to  intervening  and  obstructing  mountain  ranges,  tend 
greatly  to  reduce  the  amount  of  rainfall. 

Rain  or  snow  from  a  cloudless  sky  sometimes  occurs, 
and  is  called  serein  ;  it  is  nearly  always  small.  Buchan 
cites  a  case  from  the  experience  of  Sir  J.  C.  Ross  (the 
famous  Arctic  traveller),  on  Christmas  Day,  1839,  near 
Trinidad,  when  a  light  shower  of  nearly  an  hour  pre- 
vailed without  a  cloud  in  sight.  Similar  cases  have 
not  been  infrequent  in  the  United  States,  where  over 
twenty  have  been  observed.  It  often  suggested  that 
the  rainfall  may  be  from  thin  and  translucent  clouds. 
Professor  T.  Russell,  in  examining  nearly  one  hundred 
cases  of  rain  and  snow  from  a  clear  sky,  f oi:nd  that  the 
larger  number  occurred  "  on  the  southwest  side  of  an 
area  of  low  barometer,  ...  at  a  distance  of  about  five 
hundred  miles  from  its  centre."  Frequently  high 
winds  prevail,  so  that  the  snow  could  be  carried  from  a 
cloudy  region  in  the  upper  air. 

On  June  30th,  1877,  a  heavy  shower  at  Yevay,  Ind., 
lasting  five  minutes,  fell  from  an  apparently  cloudless 
sky.  The  rain-drops  were  of  large  size,  and,  as  caught 
on  a  sheet  of  blotting-paper,  made  circles  two  and  a 
half  inches  in  diameter.  Nearly  three  fourths  of  an 
inch  of  snow  fell  from  a  clear  sky  on  March  15th, 
1885,  at  Bloomington,  111. 

In  the  experience  of  the  author  at  Fort  Conger, 
Grinnell  Land,  81°  44'  N.,  snow  or  frost  fell  almost  daily 
during  the  prolonged  cold  spells  in  midwinter,  when 
spiculse  of  frost  appeared  to  be  continually  in  suspen- 
sion in  the  mid-air.  This  snowfall  and  frost  phenom- 
ena were  attributed  to  the  solid  condensation  of  the 


AMERICAN   WEATHER.  73 

aqueous  vapor  of  the  comparatively  warm  upper  air 
by  the  layers  being  successively  chilled  partly  by 
radiation  and  partly  by  contact  with  the  cold  underly- 
ing strata.  It  was  invariably  the  case  during  prolonged 
cold  that  the  upper  strata  of  air,  as  shown  by  observa- 
tions on  adjacent  mountains,  were  always  warmer  than 
at  the  bases. 

There  are  occasional  instances  in  which  black,  yel- 
low, or  golden  rain  are  reported,  as  well  as  showers 
containing  fish  and  animalculse  and  insects  of  various 
kinds.  In  all  these  cases  the  foreign  constitutents  and 
color  of  the  rain  or  snow  are  due  to  impurities  gathered 
from  the  surface  of  the  earth. 

In  March,  1879,  several  instances  of  yellow  rain  or 
snow  occurred  in  the  United  States.  At  South  Bethle- 
hem, Penn.,  during  the  night  of  March  16th  there  was 
a  slight  fall  of  snow  in  that  section,  and  on  the  next 
morning,  when  the  snow  had  melted,  a  yellow  deposit 
was  found  covering  the  ground,  more  or  less.  Upon 
examination  the  deposit  was  found  to  be  the  pollen  of 
pine  trees.  The  Signal  Corps  observer  at  New  Orleans 
reported  light  showers  on  the  17th,  and  stated  that  "  a 
peculiar  feature  of  the  rain  was  its  yellow  color,  which 
was  due  to  large  quantities  of  the  pollen  of  the  cypress 
trees  floating  in  the  atmosphere."  At  Lynchburg, 
Ya.,  yellow  rain  fell  on  March  21st,  1879,  a  sample  of 
which  was  transmitted  to  the  Surgeon-General  United 
States  Army  for  microscopical  examination.  Major  J. 
J.  Woodward,  Surgeon  United  States  Army,  reported 
that  ' '  the  yellow  powder  which  gives  it  its  physical 
properties  consists  entirely  of  the  characteristic  triple- 
grained  pollen  of  the  pine.  The  pine  woods  in  the 
region  around  Lynchburg  had  been  in  blossom,  I  be- 
lieve, for  some  days  previous  to  the  20th,  and  the  di- 
rection of  the  wind  at  the  time  should  indicate  where 


74  AMERICAN   WEATHER. 

the  pollen  came  from.  Under  favorable  circumstances, 
however,  the  pollen  may  be  carried  for  long  distances, 
so  that  its  source  is  not  necessarily  near  the  town." 

Professor  Weber  gives  an  account  *  of  golden  snow 
on  February  27th,  1877,  in  Peckeloh,  Germany.  He 
says: 

"  The  snow  did  not  appear  white  but  yellow,  and  a 
kind  of  yellow  which  gave  the  appearance  of  a  surface 
strewn  with  gold-dust.  I  took  up  some  of  the  snow, 
put  it  into  a  porcelain  dish,  and  allowed  the  snow-water 
to  evaporate.  A  delicate  yellow  film  settled  upon  the 
sides  of  the  dish,  very  evenly  distributed." 

GREEN  and  RED  snow  are  to  be  found  in  a  few  parts  of 
the  world,  principally  in  the  Arctic  regions,  the  color 
being  due  to  minute  organisms  called  Protococcus  ni- 
valis.  The  most  extensive  deposits  of  red  snow  known, 
situated  near  Cape  York,  Greenland,  were  discovered 
by  Captain  John  Ross,  R.N.,  in  1818,  from  whom  the 
hills,  owing  to  this  snow,  received  the  fanciful  name  of 
Crimson  Cliffs.  The  color,  however,  as  seen  by  the 
author,  is  a  faint,  dirty,  dull  red,  and  not  crimson. 

BAIN   GAUGES. 

Rain  gauges  for  ascertaining  the  quantity  of  rain 
which  falls  are  of  various  forms,  the  simplest  being 
the  metallic  cylinder  of  uniform  diameter.  The  rain- 
water caught  in  this  gauge  is  measured  by  a  small  glass 
tube,  on  which  the  relative  proportions  are  scaled,  so 
that  the  quantity  caught  may  be  measured  to  the  hun- 
dredth of  an  inch.  The  standard  gauge  of  the  Signal 
Service  is  eight  inches  in  diameter,  and  has  a  receiving 
area  of  fifty  square  inches.  The  tube  of  the  gauge  de- 


See  Klein's  WocJienschrift,  1877,  pp.  130,  131. 


AMERICAN   WEATHER. 


75 


taches  from  tlie  lower  part, 
as  is  shown  in  Fig.  14  ;  the 
reservoir  is  a  brass  tube, 
with  an  area  of  only  one 
tenth  of  the  receiving  fun- 
nel, so  that  every  hun- 
dredth of  an  inch  of  rain 
caught  fills  the  reservoir  to 
the  depth  of  one  tenth  of 
an  inch.  Gauges  from  three 
inches  upward  are  satis- 
factory for  rain  observa- 
tions, but  those  of  less  di- 
ameter are  thought  to  reg- 
ister too  little. 

Self  -  registering  rain 
gauges  are  generally  com- 
plex, and  are  apt  to  work 
with  some  degree  of  irregu- 
larity. The  Eccard  Gauge, 
shown  in  Fig.  15,  contains 
in  the  reservoir  a  float 
counterbalanced  over  a 
wheel  with  a  certain  weight, 
which,  as  the  rain  is  gath- 
ered, closes  an  electric  cir- 
cuit for  each  hundredth  of 
an  inch  that  falls,  and  by  a 
simple  mechanism  raises 
the  weight  so  as  to  be  in 
position  to  record  the  next 
hundredth. 

The  gauge  adopted  by  the 

Signal  Service,  a  standard  gauge  to  which  is  attached 
the  mechanism  devised  by  Professor  Marvin,  is  shown 


FIG.  14.— VERTICAL  SECTION  OF 
SELF-RECORDING  RAIN  GAUGE. 


76 


AMERICAN  WEATHEK. 


in  Fig.  14.     The  chain  connecting  the  weight  in  the 
reservoir  runs  over  a  wheel  which  has  notched  teeth 

fitting  into  the  links  of 
the  chain.  Whenever  a 
tenth  of  an  inch  falls,  the 
wheel  turns  one  tenth, 
and  in  doing  so  makes 
and  breaks  an  electric 
circuit  by  mechanism 
similar  to  that  in  use  on 
the  self-registering  ane- 
mometer. Every  tenth 
of  an  inch  of  rain  is  thus 
recorded  by  electricity. 
See  Fig.  11.  The  eleva- 
tion of  the  rain  gauge 
above  the  ground  was 
long  thought  to  be  an 
important  point  in  its  ex- 
posure, as  the  idea  was 
advanced  that  the  amount 
of  rain  which  fell  upon 
the  ground  was  consid- 
erably greater  than  that 
which  fell  upon  surfaces 
at  considerable  elevation. 
Later  investigations  have 
shown  that  less  rain— 
from  four  to  ten  per  cent 
—is  gathered  from  in- 
struments exposed  on  the 

roofs  of  houses  and  other 
FIG.  IS.-ECCABD'S  RAIN  GAUGE.      ^  ^^   through  the 

action  of  the  wind,  the  eddies  of  which,  acting  near 
the  gauge,  cause  the  rain  to  blow  out  of  the  receiver. 


AMERICAN   WEATHER.  77 

Experiments  go  to  show  that  a  gauge  exposed  in  the 
middle  of  a  large  level  surface,  at  considerable  eleva- 
tion, will  catch  as  much  rain  as  one  on  the  surface  of 
the  ground.  It  is  difficult,  however,  to  obtain  large 
level  surfaces  at  high  elevations,  so  that  the  best  gen- 
eral exposure  of  a  rain  gauge  is  an  open  field,  with 
the  top  of  the  gauge  from  eighteen  to  twenty-four 
inches  from  the  surface  of  the  ground. 

SNOW   AND   HAIL. 

Whenever  the  condensation  of  aqueous  vapor  takes 
place  in  temperatures  below  32°  F.,  the  deposit  is  made 
in  solid  condition,  known  as  snow  or  hail. 

Snow  is  caught  in  a  simple  gauge,  the  diameter  of 
which  is  uniform  from  top  to  bottom,  and  the  contents 
when  melted  are  measured  either  in  the  original  rain 
gauge  or  in  a  receiving  reservoir,  the  ratio  of  which  is 
generally  one  to  ten,  as  compared  with  the  receiving 
surface  of  the  snow  gauge.  In  general  it  is  estimated 
that  ten  inches  of  snow  make  one  inch  of  rain  ;  but  this 
must  be  considered  as  only  approximately  correct,  since 
the  density  and  moisture  of  the  snow  has  much  to  do 
with  the  quantity  of  the  water  yielded. 

Snow  is  made  up  of  separate  crystals,  most  of  which 
are  of  great  beauty.  The  forms  are  always  hexagonal, 
either  of  simple  or  compound  forms,  and  great  variety. 
When  the  snow  is  light  and  the  weather  cold,  the  crys- 
tals, if  caught  upon  any  soft  material,  can  be  easily  and 
conveniently  observed  either  by  the  naked  eye  or  under 
a  magnifying-glass.  When  thus  caught  the  crystals 
are  very  regular  and  unbroken. 

The  experience  of  the  author  at  Fort  Conger  showed 
that  during  any  single  storm  the  crystals  were  invari- 
ably of  the  same  form,  but  possibly  combinations  of 
two  forms  may  occur.  When  the  temperature  is  very 


78  AMERICAN  WEATHER. 

near  32°,  so  that  the  flakes  are  damp  and  the  snow 
falls  heavily,  or  is  blown  much  by  the  wind,  the  crys- 
tals are  broken,  and  the  separate  flakes  unite  to  form 
large  masses  of  snow.  One  of  these  compound  snow- 
flakes  of  remarkable  size  is  said  to  have  fallen  at  Chap- 
ston,  Wales,  January  7th,  1888,  measuring  3. 6  inches 
in  length,  1.4  in  breadth,  and  1.3  in  thickness,  and 
when  melted  gave  2i  cubic  inches  of  water. 

Hail  falls  rather  in  the  shape  of  ice  than  snow. 
There  is  a  kind  of  soft  hail,  rounded  pellets  and  of 
very  soft  grain,  which  falls  in  winter  or  spring.  This 
seems  to  be  rather  frozen  sleet,  which  itself  is  a  mix- 
ture of  snow  and  rain,  rather  than  true  hail.  A  dis- 
tinction is  made  between  this  soft  hail,  as  it  is  called, 
and  true,  hard  hail,  by  meteorologists  abroad  ;  in  the 
United  States  this  distinction  is  not  always  made. 

The  true  hard  hail  is  usually  composed  of  alternate 
concentric  layers  of  hard,  transparent,  and  soft  opaque 
ice.  The  stones,  although  of  an  irregular  shape,  yet 
in  general  are  of  a  rounded  character. 

Several  instances  are  mentioned  when  remarkable 
masses  of  ice — evidently  formed  by  hailstones  cement- 
ing together — fell  in  India. 

Dr.  Buist,  apart  from  these  masses  of  ice,  divides 
hailstones  into  three  classes  :  first,  pure  crystalline  ice 
covered  externally  with  an  opaque  coating  ;  second,, 
the  same  as  the  first,  except  that  in  its  interior  is  a 
many-pointed  star ;  third,  nearly  globular  stones 
formed  of  thin  concentric  layers  of  varying  trans- 
parency. 

The  accompanying  illustrations,  Fig.  No.  16,  A  to  E, 
show  the  structure  of  hailstones  of  various  kinds. 
Fig.  A  shows  a  hailstone  which  fell  in  the  storm  of 
May  27th,  1869,  near  Bjeloi,  Kleutsch,  Caucasus.  Figs. 
B  and  C  are  representations  of  hailstones  which  fell  at 


AMERICAN   WEATHER. 


79 


FIG.  16.— TYPICAL  FORMS  OF  HAILSTONES. 


80  AMERICAN   WEATHER. 

the  same  place  on  June  9th,  1869.  Fig.  E  shows  the 
appearance  of  a  remarkable  hailstone  which  fell,  ac- 
cording to  Captain  Delcros,  July  4th,  1819,  at  Bra- 
conniere,  in  the  northwestern  part  of  France.  In 
Fig.  D  is  shown  the  unusual  form  of  a  hailstone  2 
inches  long,  1J  inches  in  diameter,  which  fell  at 
Morgantown,  W.  Ya.,  April  28th,  1877.  This  stone 
had  an  ice  nucleus,  with  the  remainder  formed 
of  ice  and  snow,  and  with  fourteen  others  gave  an 
average  of  0.873  cubic  inches  of  water  to  each  hail- 
stone. Stones  of  this  formation  have  also  fallen  in 
France. 

The  specimens  of  hail  shown  in  section  in  A,  B,  and 
C  are  described  by  Moritz,  Director  of  the  Tiflis  Ob- 
servatory. 

They  consisted  of  concentric  layers  of  clear  ice,  alter- 
nating with  softer  porous  layers  of  less  thickness, 
around  a  very  porous  nucleus  filled  with  air  bubbles, 
and,  consequently,  opaque.  The  wreath- like  forma- 
tion of  crystals  around  the  periphery  of  the  circle  of  C 
was  in  marked  contrast  with  the  formation  inside  the 
circle,  and  must  indicate,  at  least,  two  distinctly  differ- 
ent stages  in  the  production  of  the  hail. 

C  shows  also  a  radial  formation.  There  were  six 
bright  whitish  radii  at  angular  distances  apart  of  ex- 
actly 60°.  The  spaces  between  the  radii  contained  pure 
bluish-tinted  ice,  like  glacier  ice,  filled  with  small  pear- 
shaped  cavities  with  the  apices  toward  the  centre  of 
the  hailstone.  Viewed  with  a  magnifying-glass  they 
seemed  to  be  free  from  air.  Between  the  radii  there 
were  also  groups  of  crystals  of  the  purest  ice. 

The  ice  in  E  was  much  more  densely  packed  about 
the  centre  than  in  the  other  specimens.  . 

The  formation  of  hail  occurs  under  conditions  which 
can  only  be  surmised,  but  the  alternations  of  opaque 


AMERICAN   WEATHER.  81 

and  transparent  layers  of  ice  show  conclusively  that 
very  violent  contrasts  of  temperature  must  exist,  and 
that  the  stone  passes  alternately  and  repeatedly  from 
moderately  high  to  freezing  temperatures.  It  would 
seem  probable  that  hail  is  generated  by  the  meeting  of 
cold,  very  dry,  and  possibly  descending  currents,  with 
moist  and  warm  ascending  ones. 

Various  theories  have  been  advanced  concerning  the 
formation  of  hailstones,  none  of  which,  however,  are 
considered  as  entirely  satisfactory.  Volta  broached 
the  theory  that  hail  pellets  were  in  a  state  of  constant 
oscillation  between  two  oppositely  electrified  clouds  in 
which  condensation  was  always  going  on,  and  that  the 
stones  grew  in  size  until  they  fell  to  the  earth  by  gravi- 
tation. Dove  believed  that  hail-storms  are  always 
whirlwinds  around  a  horizontal  axis,  whereby  circu- 
lating currents  carry  the  growing  hailstones  around 
and  around,  alternately  into  hot  and  cold  air,  whence 
gravitation  eventually  brings  them  to  the  earth.  The 
growth  in  size  and  structure  of  hail  is  shown  by 
its  concentric  layers,  and  makes  it  evident  that 
the  stone  passes  at  least  as  many  times  as  it  has 
separate  layers  from  a  stratum  of  air  having  a  high 
temperature  to  one  having  a  correspondingly  low 
one. 


CHAPTER  VIII. 

DISTRIBUTION   OF   PRESSURE. 

THE  distribution  of  atmospheric  pressure  over  the 
Northern  Hemisphere  for  the  year  is  shown  by  Chart  I. 
The  great  meteorologist,  Alexander  Buchan,  first  pub- 
lished similar  isobaric  charts  for  the  globe  in  1869. 
The  surprising  industry  of  Buchan  made  this  compila- 
tion possible,  while  his  acute  mind  drew  general  and 
accurate  deductions  from  his  enormous  mass  of  data, 
the  most  important  of  which  was  the  indissoluble  asso- 
ciation of  winds  with  variations  of  atmospheric  pres- 
sure. This  discovery  resulted  in  proving  conclusively 
that  the  distribution  of  pressure  and  its  attendant 
variations  are  closely  interrelated  with  the  temper- 
ature of  the  atmosphere. 

The  distribution  of  atmospheric  pressure  is  generally 
asserted  to  depend  on  the  superheated  air  near  the 
equator  expanding  and  rising  vertically,  so  that  at 
higher  levels — say  10,000  to  15,000  feet — the  pressure  is 
greater  than  at  a  corresponding  elevation  in  high  lati- 
tudes. Such  inequalities  of  pressure  must  result  in  a 
tendency  of  the  air  to  flow  from  the  equator  toward 
the  poles.  It  is  further  set  forth  that,  on  account  of 
the  spherical  shape  of  the  earth,  the  air  is  crowded,  as 
the  meridians  converge,  into  narrow  channels,  and 
finally  forced  down  to  the  earth  near  the  30th  parallel, 
where  calms  and  high  pressures  ensue. 

The  author  believes  that  to  these  causes  must  be 
added  another,  perhaps  of  much  minor  importance, 


Mean  Annual  Atmospheric  rressi 


>verinei>orinern  tiemispnere. 


AMERICAN   WEATHER.  83 

the  effect  of  enormous  masses  of  cold  dense  air,  which, 
moving  from  high  into  middle  latitudes,  must  necessa- 
rily tend  to  facilitate  the  movement  of  the  upper  air 
currents  poleward. 

Whatever  simple  principle  underlies  the  primary 
movement  of  the  atmosphere,  it  is  necessarily  interfered 
with  and  modified  by  complications  arising  not  only 
from  areas  superheated  in  some  instances,  or  chilled 
intensely  by  radiation  in  others,  but  also  from  the 
configuration  of  the  earth  in  cases  of  immense  moun- 
tain ranges,  as  the  Himalaya,  Caucasus,  Andes,  and 
Rocky  Mountains ;  sandy  deserts,  such  as  the  Sahara 
and  Gobi,  or  by  great  interior  basins,  as  in  the  United 
States. 

Professor  Mohn  has  plainly  set  forth  in  his  admir- 
able book*  that  the  barometer  is  high  (1)  when  the  air 
is  cold  ;  (2)  when  the  air  is  dry  ;  (3)  when  itn  upper 
current  sets  toward  an  area  ;  also  that  the  barometer  is 
low  (1)  when  the  lower  strata  of  air  are  heated  ;  (2) 
when  the  air  is  damp  ;  (3)  when  the  air  has  an  upward 
movement. 

Buys  Ballot's  law,  which  will  be  referred  to  later, 
shows  the  relation  of  wind  to  pressure,  so  that  if  the 
distribution  of  atmospheric  pressure  is  known,  the 
direction  of  the  wind,  which  arises  from  differences  of 
pressure,  can  be  told,  and  vice  versa. 

The  annual  pressure  is  shown  by  Chart  I.  for  the 
Northern  Hemisphere  ;  it  rests,  as  do  all  such  maps,  on 
Buchan's  early  work,  yet  material  changes  have  been 
made  from  original  data  of  late  years.  The  lines  of 
mean  pressure  over  the  Atlantic  Ocean  have  been 
drawn  from  international  observations,  1881-83,  inclu- 
sive, and  in  consequence  the  lines  are  less  hypothetical 


Grundzilge  der  Meteorologie, 


84  AMERICAN  WEATHER. 

than  usual,  while  those  for  the  United  States  are  from 
means  of  fifteen  years'  observations. 

All  the  isobars  on  Chart  No.  I.  are  drawn  from  ob- 
servations reduced  to  the  level  of  the  sea,  but  since  the 
mean  annual  temperature  is  used  as  the  temperature 
argument  in  such  reduction,  they  are  approximative^ 
correct. 

It  will  be  observed  that  there  are  two  areas  of  high 
pressure.  One,  at  or  above  30.1  inches,  in  the  middle 
latitudes — extending  as  a  band  between  the  20th  and 
40th  parallels,  from  the  Atlantic  coast  of  the  United 
States  eastward  to  the  shores  of  North  Africa  and 
Portugal — is  quite  permanent  throughout  the  year, 
while  the  other,  in  the  interior  of  Asia,  with  a  mean 
pressure  above  30.2  inches,  owes  its  prominence  to  the 
very  high  winter  pressures.  There  are  three  areas  of 
low  pressure,  the  most  important  of  which  exists  in 
the  vicinity  of  Iceland,  about  29.6,  while  secondary 
minima  are  found  in  the  Aleutian  Archipelago  slightly 
below  29.7,  and  in  India  about  29.8  inches. 

It  is  doubtless  true  that  there  are  regular  and  pe- 
riodic changes  in  the  atmospheric  pressure  from  month 
to  month,  which  are  more  or  less  masked  by  great  ac- 
cidental atmospheric  variations  attendant  upon  storms. 
These  changes  are  called  the  annual  fluctuation.  By 
joining  the  tops  of  lines  of  different  heights,  represent- 
ing the  mean  monthly  heights  of  the  barometer  at  any 
particular  place,  we  have  a  curve  showing  the  annual 
fluctuation  of  the  pressure  at  that  place. 

The  annual  fluctuations  of  atmospheric  pressure  may 
be  classified  under  two  grand  divisions  or  types,  the 
first  of  which  is  expressed  by  a  curve  with  a  single  in- 
flection, while  the  last  is  in  the  form  of  a  curve  with 
two  inflections  or  bends.  The  single  inflection  curve 
fluctuations  are  most  general,  while  the  double  inflec- 


AMERICAN   WEATHER.  85 

tion  curve  in  the  Northern  Hemisphere  obtains  in  the 
polar  or  sub-polar  regions,  in  Europe,  Northern  Africa, 
and  over  a  part  of  the  Atlantic  Ocean.  These  annual 
atmospheric  waves,  with  their  crests  and  troughs,  must 
move  over  the  Northern  Hemisphere  somewhat  in  the 
same  manner  as  the  waves  of  high  pressure,  treated  of 
later  as  cold  waves,  move  throughout  the  winter  months 
from  the  interior  of  the  American  Continent  to  the 
Atlantic  seaboard.  Doubtless,  too,  one  simple  law  de- 
pendent to  a  greater  or  less  extent  on  the  relative  posi- 
tions of  the  earth  and  sun  underlies  this  annual  fluc- 
tuation. But  barometric  data  now  available  has  not 
yet  been  sufficiently  analyzed  to  permit  any  simple  ex- 
pression of  this  law. 

This  annual  fluctuation  of  the  atmospheric  pressure 
is  a  difficult  problem,  which  has  not  been  fully  solved 
for  the  entire  Northern  Hemisphere.  Personal  investi- 
gations by  the  author  show  it  to  be  more  than  probable 
that  the  maximum  pressure  occurs  for  the  year  over 
British  America  and  part  of  Greenland  in  April,  and 
that  it  moves  slowly  southeastward,  covering  Iceland, 
Norway,  and  Sweden,  and  the  northern  portion  of  the 
British  Isles  in  May.  The  movement  of  this  air  far- 
ther southward  across  Europe  and  Africa  is  marked 
by  a  secondary  maximum  in  June  and  July,  while  the 
maximum  for  Central  Africa  apparently  occurs  in 
August.  This  indicates  that  a  part  of  these  maxima 
pressures  are  due  to  a  movement  southeastward  of 
cold  air,  chilled  by  the  radiation  of  the  long  polar 
night  of  high  latitudes.  A  secondary  maximum  in 
November  covers  the  greater  part  of  the  Arctic  circle, 
whence,  the  air  moving  southward,  gives  a  primary 
maximum  over  Europe  and  the  greater  portion  of  India 
in  December.  The  rest  of  Asia  has  a  well-marked 
maximum  in  January  and  February,  during  which 


86  AMERICAN   WEATHER. 

month  the  greatest  pressure  also  obtains  over  the 
greater  part  of  the  United  States,  Northern  Africa,  and 
the  Atlantic  Ocean.  The  principal  minimum  occurs  over 
Asia  in  July,  excepting  in  the  greater  part  of  India, 
where  it  obtains  in  June.  The  principal  minimum  of 
April  covers  the  United  States,  the  Atlantic  Ocean,  and 
the  Mediterranean  Sea,  and  adjacent  regions  between 
the  30th  and  40th  parallels  of  latitude. 

The  curve  showing  the  annual  oscillations  at  Fort 
Conger  coincides  closely  and  regularly  with  the  ob- 
servations of  the  many  expeditions  in  Arctic  America 
since  the  commencement  of  this  century.  This  marked 
double  oscillation  doubtless  obtains  annually  at  the 
north  geographical  pole,  and  hence  is  styled  the  polar 
type.  A  principal  maximum  in  April  gives  way  rap- 
idly to  the  primary  minimum  in  July,  followed  by  a 
well-marked  and  complete  secondary  wave,  the  crest  of 
which  appears  in  November  and  the  trough  in  Janu- 
ary. A  second  type,  called  the  American,  a  single  an- 
nual curve,  obtains  in  America  and  in  parts  of  Europe 
and  over  the  Mediterranean,  where,  however,  it  is  more 
or  less  modified  by  the  grand  polar  type.  In  the 
American  type  the  single  maximum  of  January  rapidly 
gives  way  to  a  strongly  marked  depression  in  April,  its 
recovery  to  the  January  maximum  being  slow  but  sub- 
stantially uninterrupted. 

The  third  type  is  called  the  Asiatic,  and,  like  the 
American,  consists  of  a  single  annual  wave.  The  crest 
covers  India  and  the  valley  of  the  Yenisei  in  Decem- 
ber, but  it  is  not  simultaneous  for  all  Asia,  as  the  wave 
moves  eastward,  reaching  the  Pacific  coast  and  the  ex- 
treme southeastern  part  of  Asia  in  February.  The 
minimum  pressure  of  the  Asiatic  type  obtains  in  July 
for  the  greater  part  of  that  continent,  although  in 
Southern  India  it  prevails  a  month  earlier. 


AMERICAN  WEATHER.  87 

The  observations  at  Honolulu,  Hawaii,  in  connection 
with  those  of  the  Aleutian  Archipelago,  seem  to  indi- 
cate a  fourth  type.  In  this  type,  also  a  single  wave, 
the  June  or  July  maximum  wanes  steadily  to  a  Janu- 
ary minimum  over  those  portions  of  the  North  Pacific 
Ocean  where  it  is  not  complicated  by  the  advance  of 
the  Asiatic  wave  eastward  in  February.  While  the 
maximum  of  the  Atlantic  occurs  generally  in  July,  as 
on  the  Pacific,  yet  its  maximum  in  middle  latitudes, 
as  shown  by  Bermuda  and  Delgada,  obtains  in  April, 
as  in  the  United  States,  and  the  influence  of  the  polar 
secondary  wave  appears  at  both  stations  in  the  tendency 
to  a  secondary  curve,  with  minimum  in  October  and 
maximum  in  February. 

While  the  movements  of  the  atmospheric  pressure 
from  month  to  month,  as  here  outlined,  appear  to  be 
borne  out  by  the  international  simultaneous  observa- 
tions for  the  past  ten  years,  yet  it  must  be  admitted 
that  more  observations,  especially  in  lower  latitudes 
and  over  the  Pacific  Ocean,  are  necessary  to  determine 
how  far  these  changes  are  regular  and  periodic.  As 
bearing  out  the  views  here  expressed — see  Fig.  No.  17— 
are  presented  typical  curves  of  atmospheric  pressure 
from  observations  reduced  for  temperature  of  barom- 
eter and  instrumental  error  only,  so  that  the  phe- 
nomena can  be  studied  with  reference  to  the  actual 
changes  of  pressure,  and  not  with  reference  to  the 
imaginary  height,  as  found  by  reduction  to  the  sea 
level,  especially  an  important  consideration  where  the 
elevation  of  the  station  is  great. 

As  typical  annual  Asiatic  curves  of  atmospheric  pres- 
sure, there  appears,  in  Fig.  No.  17,  those  of  Pekin,  on 
the  coast  of  China,  Yeniseisk,  in  the  interior  of  Siberia, 
and  Agra  in  the  interior  of  India.  These  are  curves  of 
great  ranges,  with  a  single  inflection,  with  their  maxi- 


AMERICAN  WEATHEK. 


Annual  fluciuations  of  atmospheric  pressure. 


FIG.  17. 


AMERICAN   WEATHER.  89 

mum  in  January  and  their  minimum  in  June  and  July. 
The  curves  of  Portland,  Ore.,  St.  Louis,  Mo.,  and  Salt 
Lake  City,  Utah,  are  also  curves  with  single  bends, 
with  their  maxima  in  January  and  their  minima  in 
April,  except  at  Portland,  where  it  occurs  in  August. 
The  curve  at  Honolulu,  Hawaiian  Islands,  is  a  single 
wave,  with  its  minimum  phase  in  February  and  its 
maximum  in  May  or  June.  The  typical  Arctic  curves 
—with  double  inflections — are  those  of  Fort  Conger 
and  Stykkisholm,  the  pressure  rising  from  the  primary 
minimum  in  January  to  the  primary  maximum  in 
April  or  May.  At  Fort  Conger  a  secondary  minimum 
in  July  is  followed  by  a  very  well-marked  maximum 
in  November,  but  at  Stykkisholm  the  secondary  mini- 
mum is  delayed  until  October,  and  the  November 
maximum,  while  well  defined,  is  not  as  prominent  as 
that  of  Fort  Conger.  The  Ponta  Delgada  and  Bermuda 
are  typical  Atlantic  curves,  with  the  primary  minimum 
in  April  and  the  primary  maximum  in  July,  followed 
by  a  secondary  wave,  with  its  trough  in  November 
and  its  crest  in  February.  At  Berlin  the  wave  is  also 
double,  falling  from  its  primary  maximum  in  January 
to  its  primary  minimum  in  April.  The  irregular 
curve  during  the  rest  of  the  year  shows  a  secondary 
maximum  in  September  and  minimum  in  December. 

Over  the  United  States  the  actual*  atmospheric 
pressure,  as  shown  by  the  mean  of  fifteen  years'  ob- 
servations, is  greatest  in  January,  in  which  month  the 
maximum  is  reached  from  the  entire  Eocky  Mountain 
slope  eastward  to  the  Atlantic  coast,  except  over  a 
portion  of  the  lake  region.  The  most  important  de- 
parture from  this  is  over  the  immediate  Rocky  Moun- 


*  By  the  actual  is  meant  the  recorded  pressure,  reduced  for  tempera- 
ture of  the  barometer,  etc.,  but  not  to  the  sea  level  or  any  other  plane. 


90  AMERICAN  WEATHER. 

tain  range,  in  Arizona  and  in  a  part  of  New  Mexico, 
where  the  maximum  occurs  in  July  or  August.  In- 
deed, so  divergent  are  the  conditions  over  the  Rocky 
Mountain  stations  (all  above  4000  feet)  from  the  gen- 
eral conditions,  that  the  minimum  obtains  in  January. 
California,  with  a  January  maximum  throughout  its 
whole  extent,  shows  its  special  climatic  condition  by 
differing  from  the  adjacent  regions  to  its  north  or  east, 
since  Oregon,  Washington,  and  the  Great  Interior 
Basin  have  their  greatest  pressures  in  November. 

The  mean  yearly  pressure  over  the  United  States, 
shown  in  a  general  manner  on  Chart  I.,  ranges  between 
30  and  30.1  inches  when  reduced  by  ordinary  methods 
to  sea  level.  Such  reductions,  however,  are  only  ap- 
proximate, owing  to  the  fact  that  the  greater  part  of 
the  United  States  is  more  than  1500  feet  above  the 
sea.  The  temperature  argument  for  reduction — a  very 
important  factor — can  quite  safely  be  assumed  to  be  the 
same  as  the  mean  annual  temperature  of  the  place  of  ob- 
servation. The  use  of  the  current  temperature  of  the  air 
at  the  station  for  reducing  monthly  or  daily  observa- 
tions to  sea  level  has  led  to  grave  errors. 

The  result  of  this — the  current  method  of  reducing 
barometer  observations  at  high  stations  in  the  plateau 
region  of  the  Rocky  Mountains  to  the  level  of  the  sea— 
has  been  to  give  an  erroneous  idea  of  the  actual  state 
of  pressure  in  that  region,  such  reductions  indicating 
the  pressure  in  January  to  be  relatively  high  when  in 
reality  the  actual  pressure  is  much  lower  than  at  other 
times  of  the  year. 

The  necessity  is  obvious  of  reducing  barometer  ob- 
servations to  a  common  plane  for  the  purpose  of  mak- 
ing weather  predictions,  where  it  is  essential  to  know 
the  gradients  of  pressure  or  difference  in  pressure  from 
place  to  place,  which  is  the  actuating  cause  or  bears 


January 

TIOH 'in  English  i-rtcfoes 


KSSLs 


AMERICAN   WEATHER.  91 

an  intimate  relation  to  the  motion  of  the  air.  But 
when  the  barometer  is  reduced  to  sea  level  with  a 
view  of  representing  the  average  condition  of  pressure 
for  that  region,  and  of  proving  a  great  increase  of  pres- 
sure and  a  consequent  accumulation  of  air  in  winter, 
it  is  certainly  misleading,  since  in  reality  there  is  a 
diminution  of  the  amount  of  air  present. 

It  results  in  representing,  from  month  to  month, 
that  the  atmospheric  pressure,  at  stations  covering  an 
area  of  several  hundred  thousand  square  miles,  is  in- 
creasing, when  it  is  actually  decreasing. 

At  Mount  Washington,  6279  feet  above  sea  level,  the 
mean  actual  barometer  in  January  is  half  an  inch  less 
than  in  July,  while  at  sea  level  in  the  vicinity  the 
January  pressure  is  higher  than  that  for  July.  This 
result  is  due  to  the  lower  average  temperature  of  Jan- 
uary contracting  the  great  body  of  the  air,  so  that  more 
of  it  is  brought  below  the  summit  of  the  mountain. 
But  if  there  were  a  great  plain  in  the  vicinity  of  the 
mountain  at  the  same  height,  it  would  obviously  be 
improper,  in  a  discussion  of  its  climatic  peculiarities, 
to  analyze  its  pressures  for  that  purpose  from  the 
point  of  view  of  their  reduction  to  the  sea  level,  yet 
such  method  of  treatment  has  heretofore  obtained  for 
the  high  plateau  regions  in  the  western  part  of  the 
United  States. 

The  author  has  preferred  to  depart  from  such  a 
method  of  representation  in  treating  the  monthly  mean 
pressures  over  the  United  States  for  January  and  April 
• — the  months  which  show,  for  the  greatest  area,  the 
maximum  and  minimum  pressures.  Charts  II.  and 
III.  are  based  entirely  on  the  actual  means — i.e.,  only 
reduced  for  the  temperature  of  the  barometer  to  32°, 
the  departures  of  January  and  April  from  the  annual 
means  of  the  actual  readings  being  used. 


92  AMERICAN  WEATHER. 

The  January  map,  Chart  II. ,  shows  plainly,  by  the 
method  of  departure  from  the  annual  mean,  the  pres- 
sure of  the  atmosphere  during  January,  which  is  the 
coldest  month  of  the  year.  The  January  minimum 
over  the  Rocky  Mountain  region  is  the  more  to  be 
noticed  since  it  has  been  insisted  on  by  some  writers 
that  the  maximum  pressures  occur  in  the  interior  of 
all  great  continents  in  January,  or  the  winter  season. 

Such  certainly  is  not  the  case  in  the  United  States, 
with  its  January  maximum  almost  unbroken  along  its 
4000  miles  of  coast,  and  no  such  maximum  between  100° 
and  120°  of  longitude  except  at  the  very  coast.  Ex- 
cepting over  a  portion  of  the  lake  region  and  the  Wash- 
ington Territory  coast,  there  is  no  part  of  the  country 
with  an  elevation  less  than  1500  feet  that  does  not  have 
its  maximum  pressure  in  January. 

This  is  what  might  be  expected,  since  the  cold,  dense, 
and  contracted  lower  strata  of  air  must  necessarily  sink 
down  and  thus  seek  the  lowest  levels.  This  is  what 
occurs,  and  the  cold,  dry  areas  of  pressure  which  move 
southward  into  the  United  States  do  not  remain  over 
the  Rocky  Mountain  region,  since  these  dense,  cold 
strata  are  not  deep  enough  to  reach  up  to  the  high 
plateaus  nor  to  overflow  the  mountain  crests  and  fill 
up  the  great  interior  basin  of  Idaho,  Utah,  and  Nevada. 
In  this  connection  it  is  further  interesting  to  note  that 
the  excess  of  the  January  mean  above  that  for  the 
year  increases  regularly  along  the  river  valleys  with 
decreasing  elevation ;  the  excess  increasing  in  the 
Missouri  Valley  from  zero  at  Poplar  River  to  .04  inch 
at  Bismarck,  .08  at  Yankton,  and  .10  inch  at  Leaven- 
worth  ;  in  the  Mississippi  Valley,  from  .07  inch  at  St. 
Paul  to  .08  at  St.  Louis  and  .10  at  New  Orleans  ;  in 
the  Ohio  Valley,  from  .05  inch  at  Pittsburg  to  .07  at 
Cincinnati  and  .08  at  Louisville ;  in  the  Tennessee 


' Atmospheric fressure 

for 

April 


0?  THB 

.TIVBRSIT 


AMEBICAN  WEATHEB.  93 

Valley,  from  .06  inch  at  Knoxville  to  .08  at  Chatta- 
nooga and  .09  at  the  junction  of  the  river  with  the 
Ohio.  This  is  clearly  the  result  of  the  cold  air  settling 
down  in  the  river  valleys,  thus  increasing  the  density 
of  the  lower  strata  of  the  atmosphere.  Over  the  whole 
of  the  region  between  the  102d  and  115th  meridians, 
including  the  Rocky  Mountains  and  parts  of  the  plateau 
region,  the  pressure  is  decidedly  lessened,  and  over 
the  whole  of  this  region  the  pressure  decreases  from 
December  to  January,  after  which  month  there  is  an 
increase  over  most  of  the  region  mentioned  until  the 
maximum  in  July.  The  greatest  excess  east  of  the 
Rocky  Mountains  is  found  in  the  southeastern  half  of 
the  Atlantic  States,  toward  which  quarter  the  cold 
areas  of  air  flowing  out  of  British  America  tend,  as 
is  shown  by  the  prevailing  north  and  northwest  winds. 
It  is  interesting  to  note  that  the  line  of  no  change  is 
substantially  coincident  with  the  contour  elevation 
lines  for  3000  feet,  which  elevation,  it  is  possible,  would 
prove  satisfactory,  as  a  plane,  to  reduce  at  least  the 
winter  observations  of  the  barometer. 

The  month  of  minimum  pressure  over  the  United 
States — see  Chart  III. — is  not  as  satisfactorily  and 
sharply  defined  as  is  that  of  the  maximum  pressure. 
Over  one  third  of  the  country  the  lowest  pressure  oc- 
curs during  the  month  of  April,  and  in  other  contigu- 
ous sections,  equal  in  area,  during  May  and  June.  It 
is  possible  that  the  means  derived  from  fifteen  years' 
observations  are  not  sufficient  to  clearly  settle  this 
question,  and  that  a  longer  series  would  show  that 
May  is  the  month  of  minimum  pressure,  except  along 
the  Pacific  and  South  Atlantic  coasts  and  over  the 
Rocky  Mountain  region,  including  the  Interior  Basin. 
The  minimum  for  California  and  Oregon,  from  fifteen 
years'  observations,  is  very  well  marked  for  August, 


94  AMERICAN  WEATHER. 

during  which  month  the  pressure  is  also  the  lowest  on 
the  Atlantic  coast  south  of  the  35th  parallel.  A  con- 
siderable portion  of  the  immediate  Rocky  Mountain 
region  has  its  lowest  pressures  during  January,  the 
month  when  it  is  theoretically  claimed  it  should  be  the 
highest. 

Variations  in  the  atmospheric  pressure  are  periodical 
(that  is,  recur  at  regular  intervals)  or  accidental  (that 
is,  result  from  influence  of  the  extraordinary  and  un- 
usual disturbances  of  the  local  atmospheric  conditions). 
The  daily  variation  is  the  most  marked  of  the  periodic 
variations,  and  it  assumes  the  greatest  regularity,  as 
well  as  the  greatest  amplitude,  near  the  equator,  and 
is  the  least  marked  in  very  high  latitudes.  At  Cal- 
cutta, according  to  Buchan,  the  primary  maximum 
occurs  at  9  A.M.  and  the  primary  minimum  at  4.30 
P.M.,  followed  by  a  secondary  phase  at  12.30  A.M.  and 
3.30  A.M.  The  amplitude  varies  from  .117  at  Calcutta, 
in  22  K,  to  .010  inch  at  Fort  Conger,  in  82  K 

Various  theories  have  been  advanced  to  explain  the 
cause  of  the  diurnal  oscillation  of  the  barometer,  none 
of  which  have  been  completely  satisfactory.  The 
diurnal  changes  in  temperature  and  in  the  quantity  of 
aqueous  vapor  present  in  the  air  are  presumed  to  ex- 
ercise the  greatest  influence.  The  idea  was  formerly 
advanced  that  the  daily  barometric  variation  entirely 
disappeared  within  the  Arctic  circle,  where  no  alterna- 
tion of  day  and  night  occurred.  Such  opinion  is,  how- 
ever, disproved  by  the  various  observations  made  with- 
in the  Arctic  circle  ;  notably  those  by  international 
polar  expeditions  at  Spitzbergen,  Point  Barrow,  and 
Fort  Conger  (see  Fig.  18).  The  comparison  of  the 
Arctic  curves  by  the  author  showed  the  great  probabil- 
ity that  at  least  one  component  of  the  diurnal  fluctua- 
tion depends  upon  other  causes  than  the  alternation 


AMERICAN   WEATHER. 


95 


Diurnal  Barometric  Oscillations 


Stations 


AM 


PM. 


.12    34,58789  30  11  121    23450789  1O  11  12 


Ft.Conq 


Tacand 


.80 


FIG.  18. 


of  day  and  night,  and  that  this  wave  does  not  always 
follow  the  sun  in  the  rotary  movement  of  the  earth. 

In  charting  the  hourly  oscillations  from  a  number 
of  Arctic  stations,  it  was  found  that  on  maps  with  refer- 
ence to  local  time  the  curves  were  thoroughly  discord- 
ant. When  charted  on  simultaneous  time,  for  fifteen 
out  of  twenty -four  hours  the  values  of  the  departures, 
either  plus  or  minus,  are  in  accord,  but  when  charted 
on  local  time,  at  no  single  hour  do  the  values  have  the 
same  sign  at  all  stations. 

Observations  have  not  been  sufficiently  numerous  to 
determine  accurately  the  diurnal  variation  in  the  barom- 
eter for  the  United  States,  except  at  a  few  scattered 


yb  AMERICAN   WEATHER. 

stations.  For  the  country  generally  it  may  be  said, 
however,  that  the  amplitude  ranges  from  .040  to  at 
least  .100  inch. 

It  is  in  general  a  correct  statement  that  the  daily 
amplitude  of  the  barometer  decreases  in  the  United 
States  with  increase  of  latitude,  but  to  this  decrease 
there  are  important  and  well-marked  interruptions. 
East  of  the  Rocky  Mountains  the  amplitude  increases 
to  about  parallel  31°  N.,  whence  the  decrease  is  regular 
and  constant  to  the  northward.  From  Georgia  and 
Tennessee  westward  to  Central  Texas  there  is  a  large 
area  of  country  over  which  the  range  appears  to  be 
considerably  larger  than  that  to  the  north  and  south. 
For  instance,  the  range  increases  from  .076  inch  at 
Jacksonville  to  .101  at  Augusta  ;  from  .090  at  Pensa- 
cola  to  .099  at  Montgomery  ;  from  .090  at  New  Orleans 
to  .104  at  Shreveport,  and  .093  at  Memphis  and  Nash- 
ville ;  and  from  .073  inch  at  Brownsville  to  .090  at  San 
Antonio,  and  .110  at  Fort  Stockton.  These  values 
have  not  been  determined,  however,  with  very  great 
accuracy,  but  observations  prove  quite  conclusively 
that  over  this  section,  for  a  considerable  distance  in- 
ward from  the  Gulf  coast,  the  amplitude  increases  to 
the  northward.  A  portion  of  this  irregularity  may  be 
attributed  to  the  distance  from  the  sea  or  great  lakes, 
as  the  amplitude,  possibly  a  result  of  a  continental 
climate,  is  .100  at  Montgomery,  Ala.,  .104  at  Fort  Stock- 
ton, Tex.,  and  .078  at  Leaven  worth,  Kan.,  and  Win- 
nemucca,  Nev.  Other  causes,  however,  than  distance 
from  the  sea  alone  must  obtain,  since  among  the 
smallest  amplitudes  of  the  United  States  are  those  of 
Dakota  and  Northwestern  Minnesota — .023  at  St.  Yin- 
cent  and  .040  at  Bismarck.  The  smallest  known  varia- 
tion elsewhere  in  the  United  States  is  .027  inch  at 
Thunder  Bay  Id.?  Mich, 


AMERICAN   WEATHER.  97 

The  amplitude  over  Nevada,  Idaho,  and  other  por- 
tions of  the  Interior  Basin  and  plateau  districts  of  the 
United  States,  also  increases  from  the  great  lakes  west- 
ward and  from  the  Pacific  Ocean  to  the  eastward. 

Fig.  No.  17  shows,  charted  on  local  time,  the  diurnal 
curve  for  various  stations  in  the  United  States.  The 
curves  for  Washington  and  Toronto  are  much  better 
determined  than  the  others.  The  Fort  Conger  curve 
is  added  to  show  that  the  diurnal  variation  obtains 
near  the  North  Pole. 

Next  in  order  comes  the  monthly  variation  or  range. 
The  mean  montlily  range  of  the  barometer  in  the 
United  States  increases  quite  regularly  with  latitude, 
and  decreases  slightly  and  somewhat  irregularly  with 
increasing  longitude.  The  ranges  vary  from  0.35  inch 
at  Key  West  to  1.16  at  Eastport,  on  the  Atlantic  coast ; 
from  0.36  inch  at  San  Diego  to  0.78  at  Tatoosh  Island, 
on  the  Pacific  coast ;  and  from  0.55  inch  at  Browns- 
ville to  1.02  at  St.  Vincent,  on  the  97th  meridian. 

The  range  is  least  for  the  month  of  July  almost 
without  exception  throughout  the  country  ;  but  while 
the  greatest  mean  range  occurs  in  January  as  a  rule, 
yet  at  occasional  points  the  maximum  obtains  in  De- 
cember or  February. 

The  annual  range  in  the  United  States  rarely  exceeds 
one  inch,  except  to  the  northward  of  the  40th  parallel 
or  along  the  immediate  Atlantic  coast.  The  annual 
range  at  Toronto,  Canada,  for  forty- six  years,  is  1.65 
inches,  with  an  absolute  range  of  2.77  inches. 

The  absolute  ranges  are  naturally  connected  with 
violent  atmospheric  disturbances,  and  the  lowest  barom- 
eter readings  as  a  rule  occur  either  in  connection 
with  the  permanent  areas  of  low  pressure  in  the  vicin- 
ity of  Iceland  in  the  Atlantic,  or  of  the  Aleutian 
Islands  in  the  Pacific  Ocean.  At  Unalaska,  January 


98  AMERICAN  WEATHER. 

21st,  1879,  a  reading  of  27.70  was  noted,  and  at  Stykkis- 
liolm  27.91  was  recorded  February  1st,  1877. 

Even  more  remarkable  readings  have  been  noted  in 
connection  with  the  typhoons  of  the  China  Sea  and  the 
cyclonic  storms  of  the  Atlantic.  On  September  27th, 
1880,  the  ship  "  Chateaubriand,"  in  22°  N.,  121°  E.,  ex- 
perienced a  violent  typhoon,  during  which  the  barom- 
eter sank  in  four  hours  from  29.64  to  the  unprecedented 
point  of  27.04.  Wind  of  force  12,  from  the  northwest, 
was  followed  by  a  dead  calm  and  then  by  south  and 
southeast  winds,  force  12,  thus  showing  that  the  vessel 
was  in  the  centre  of  the  typhoon. 

The  following  interesting  and  unusually  low  and  high 
barometer  readings  are  recorded  :  22°  N.,  121°  E.,  near 
Grand  Turk  Island,  27.04,  September  27th,  1880; 
Ochtertyre,  Perthshire,  Scotland,  27.33,  January  26th, 
1884;  Onset  Head,  England,  27.45,  December  8th, 
1886  ;  28°  N.,  68°  W.,  "  Golden  Fleece,"  27.60,  October 
2d,  1880  ;  59°  1ST.,  24°  W.,  27.68,  January  17th,  1879, 
September,  1880  ;  Unalaska,  27.70,  January  21st,  1879  ; 
53°  N.,  25°  W.,  "Austrian,"  27.88,  November  30th, 
1878  ;  Hainan  Reefs,  E.,  27.88,  October  16th,  1880  ; 
29°  N.,  132°  W.,  27.88,  October  2d,  1880  ;  Stykkisholm, 
27.91,  February  1st,  1877 ;  41°  N.,  57°  W.,  28.00,  Octo- 
ber 29th,  1879  ;  38°  N.,  35°  W.,  28.02,  October  8th, 
1878;  49°  N.,  21°  W.,  28.08,  April  1st,  1886;  off 
Umqua,  Ore.,  28.20,  January  9th,  1880  ;  North  Unst, 
28.21,  March  1st,  1880  ;  28°  N.,  88°  W.,  28.38,  Septem- 
ber 9th,  1882  ;  Nagasaki,  28.50,  August  4th,  1880 ; 
Halifax,  28.59,  November  20th,  1879  ;  Reunion,  28.62, 
March  20th,  1879  ;  Mauritius,  28.62,  March  21st,  1879  ; 
Kingston,  Jamaica,  28.93,  August  18th,  1880  ;  Crooked 
Island  Passage,  28.94,  September  4th,  1882  ;  Trinidad 
(lowest),  29.04,  September  2d,  1878  ;  Bermuda,  29.14, 
August  30th,  1880  ;  N,  W.  Russia,  30.91,  February 


AMERICAN  WEATHER.  99 

17th,  1880  ;  Fort  Conger,  31.00,  March,  1883  ;  "  Jean- 
nette,"  31.09, 1880  ;  Barnaul,  31.21,  January  9th,  1877  ; 
Fort  Assinaboine,  31.21,  January  6th,  1886. 

The  absolute  range  for  the  United  State  varies  from 
1  to  2-J-  inches,  increasing  along  the  Atlantic  and  Pa- 
cific coasts  with  the  latitude  ;  but,  owing  to  the  cyclonic 
disturbances  prevalent  in  the  Gulf  of  Mexico,  they  are 
greatest  on  the  G-ulf  coast,  decreasing  northward  for 
several  hundred  miles,  and  then  gradually  diminishing. 

The  following  absolute  ranges  illustrate  the  United 
States  generally  in  this  respect :  San  Diego,  Cal.,  1.014 
inches  ;  Olympia,  Wash.  Terr.,  1.717  inches  ;  Key  West, 
Fla.,  1.176  inches  ;  New  York,  2.201  inches  ;  Eastport, 
Me.,  2.523  inches  ;  Brownsville,  Tex.,  1.896  inches  ; 
Chicago,  111.,  1.775  inches,  and  St.  Yincent,  Minn., 
1.786  inches. 


CHAPTER  IX. 

THE  DISTRIBUTION   OF   TEMPERATURE. 

THE  temperature  of  the  air  results  from  the  solar 
rays,  as  has  been  set  forth,  and  the  amount  of  heat  de- 
pends, not  so  much  on  the  varying  distance  of  the  sun 
during  the  year,  as  on  the  angle  at  which  these  rays 
strike  the  surface  of  the  earth.  The  sun  is  most  nearly 
vertical  in  the  United  States  at  the  summer  solstice 
in  June,  when  the  heating  powers  of  the  sun's  rays, 
being  more  nearly  vertical,  have  less  thickness  of  at- 
mosphere to  pass  through,  so  that  it  loses  less  heat 
than  when  the  inclination  is  greater,  as  has  already 
been  explained  in  Chapter  IY.  .The  solar  rays  being 
of  high  power  pass  through  the  air  with  comparatively 
small  loss  of  heat,  and  so  affect  most  materially  the 
temperature  of  the  surface  of  the  earth  ;  thus  produc- 
ing effects  which  vary  according  to  the  character  of  the 
surface  upon  which  the  solar  rays  fall.  The  immedi- 
ate surface  of  the  earth  and  its  vegetation  having  ab- 
sorbed the  heat  of  the  solar  rays,  in  turn  radiates  it 
toward  space ;  but  the  character  of  the  rays  have 
changed,  so  that  it  becomes  dark  heat,  and  conse- 
quently its  effect  in  changing  the  temperature  of  the 
atmosphere  is  very  much  greater  than  that  wrought 
directly  by  the  solar  rays.  In  consequence  of  the 
varying  changes  in  the  inclination  of  the  solar  rays 
toward  the  earth,  as  well  as  a  diminution  in  the  hours 
of  sunlight,  the  temperature  of  the  earth  changes  from 
month  to  month. 


Mean  Annual   Temper; 


Ire  of  the  Northern  Hemisphere. 


AMERICAN    WEATHER.  101 

The  annual  mean  is  derived  from  the  mean  tempera- 
ture of  the  months.  The  annual  mean  for  the  North- 
ern Hemisphere  is  shown,  with  a  fair  degree  of  accu- 
racy, on  Chart  No.  IV.  by  a  series  of  isotherms  *  drawn 
for  each  ten  degrees. 

The  temperatures  here  shown  are  not  reduced  to  sea 
level,  and  so  are  not  as  accordant  as  if  thus  reduced. 
Sea-level  isotherms,  however  useful  for  elaborate  or 
scientific  discussions  and  theories,  are  but  representa- 
tions, having  no  existence  in  nature,  and  consequently 
are  not  to  be  commended  in  a  work  of  this  scope, 
which  aims  to  present  climatic  data  in  as  simple  and 
plain  a  way  as  possible. 

A  cursory  glance  discloses  that  the  isothermal  lines 
are  not  strictly  parallel  with  the  equator ;  that  even  the 
belt  of  highest  mean  temperature  is  not  equally  bisected 
by  that  great  circle,  while  the  isotherms  are  irregularly 
and  curiously  distorted.  The  greatest  inclinations  to 
the  parallels  appear  along  the  west  coast  of  continents 
and  large  islands  in  middle  latitudes.  The  causes  of 
these  distortions  are  the  unequal  distribution  of  land 
and  water,  with  their  differing  methods  of  absorbing 
the  heat  of  the  solar  rays  ;  the  distribution  of  atmos- 
pheric pressure  referred  to  in  Chapter  VIII. ,  with  the 
resulting  prevailing  winds  ;  peculiar  land  configura- 
tions, such  as  high,  enormous  mountain  masses  and 
extensive  desert  areas,  and — by  no  means  the  least  im- 
portant— ocean  currents,  whether  surface  and  drift 


*  An  isotherm  is  a  line  whereon  all  places  have  the  same  temperature. 
This  method  of  graphically  showing  the  temperature  of  the  terrestrial 
globe  was  first  extensively  used  by  Humboldt  about  1817.  Isotherms 
take  their  name  from  the  temperature  they  indicate,  as  an  isotherm  of  32°, 
50°,  etc.  Isotherms,  when  mentioned  indefinitely,  are  understood  to  refer 
to  the  mean  temperature,  but  monthly,  daily,  and  hourly  isotherms  are 
now  in  constant  use  by  meteorologists. 


102  AMERICAN   WEATHER. 

from  the  wind,  or  permanent  from  vertical  distribution 
of  sea  temperatures. 

The  mean  temperature  of  the  land  in  equatorial 
regions  is  higher  than  that  of  the  ocean,  but  in  higher 
latitudes  reverse  conditions  obtain.  The  transfer  of 
heat  from  the  equator  by  wind  and  ocean  currents 
tends  to  equalize  the  temperatures  of  different  latitudes. 

As  bearing  on  the  oceanic  influence  a  brief  allusion 
to  the  distribution  of  sea  temperature  is  necessary. 

The  temperatures  of  both  the  surface  and  the  depth 
of  the  Atlantic  Ocean  have  been  observed  with  great 
care  during  the  past  twenty  years,  so  that  enormous  as 
is  the  expanse  of  water,  yet  a  fairly  accurate  knowl- 
edge is  now  had  from  the  equator  to  the  80th  parallel. 
The  sun's  heat  is  not  absorbed  entirely  by  the  surface 
water,  but  a  considerable  portion  passes  through  the 
upper  layer  of  the  sea,  so  that  the  solar  heat  probably 
extends  downward  about  five  hundred  feet.  The  tem- 
perature of  the  sea  follows  that  of  the  air  quite  slowly, 
so  that  its  daily  amplitude  is  considerably  less  than 
that  of  the  air.  According  to  observations  on  the  At- 
lantic seaboard  of  the  United  States,  the  sea  and  air 
throughout  the  year  fluctuate  to  about  the  same  extent 
from  Key  West  to  Southport,  "N.  C.  At  Sandy  Hook, 
however,  the  fluctuation  of  the  temperature  of  the  air, 
as  determined  from  monthly  means,  is  twenty-five  per 
centum  greater  than  that  of  the  sea,  while  at  Eastport 
the  variation  amounts  to  two  hundred  and  forty  per 
centum.  The  sea  lags  about  half  a  month  behind  the 
air  in  its  march  of  temperature  from  Key  West  to 
Southport,  N.  C.,  whence  the  retardation  increases, 
amounting  to  one  month  at  Sandy  Hook,  N.  J.,  and 
to  nearly  two  months  at  Eastport.  The  sea  averages 
about  one  degree  colder  at  Key  West,  2.5°  at  Sandy- 
Hook,  and  6.5°  at  Eastport,  Me, 


AMERICAN  WEATHER.  103 

The  sea-water  isotherms  are  much  more  regular  than 
those  of  the  air,  but  they  are  more  open  along  the  coast 
of  Africa  and  Europe  than  that  of  America,  so  that 
with  increasing  latitude  their  trend  changes  from 
nearly  east  and  west  to  northeast  and  southwest. 

The  annual  temperature  of  the  surface  of  the  sea 
ranges  from  about  75°  just  north  of  the  equator  along 
the  Gold  Coast,  to  28°  in  the  Great  Frozen  Sea  to  the 
northward  of  Grinnell  Land.  The  variation  of  mean 
temperature  is  thus  about  sixty  per  centum  of  that  of 
the  air,  which  ranges  from  — 5°  at  Fort  Conger  to  84°  at 
Massowah,  Tied  Sea. 

But  below  the  point  at  which  the  sun's  heat  ceases 
to  affect  the  sea  the  temperature  conditions  change 
most  materially.  At  the  bottom  of  the  Great  Frozen 
Sea  the  temperature  is  doubtless  about  the  same  as  at 
the  surface,  and  from  that  point  it  increases  toward 
the  equator  from  28°  to  37°  at  the  greatest  depths. 
At  a  plane  of  some  4000  feet  below  the  surface  the  ob- 
servations show  an  increase  from  37°  to  47°,  the  rise  in 
the  temperature  being  to  the  southward  till  the  30th 
parallel  is  reached,  whence  it  decreases  to  about  40° 
under  the  equator.  Along  the  European  coast  is  a 
layer  of  warm  water  at  4000  feet,  the  temperature  off 
the  Mediterranean  rising  slightly  above  50°. 

The  influence  of  the  predominance  of  water  is  best 
illustrated  by  the  isotherms  of  the  British  Isles,  where 
the  summer  temperatures  are  lowered  and  the  winter 
temperatures  raised  through  this  influence,  which  is 
re- enforced  on  the  windward  side  by  the  prevailing 
winds.  The  only  part  of  the  United  States  where  the 
climate  is  affected  by  the  oceanic  current  is  the  im- 
mediate Pacific  coast,  where  the  mild  and  equable 
temperature  results  in  part  from  the  Japan  current 
and  the  prevailing  winds  which  have  passed  over  its 


104  AMERICAN   WEATHER. 

surface.  It  is  evident  that  the  temperature  of  the 
Pacific  coast  can  be  materially  affected  by  this  cur- 
rent only  in  an  indirect  way,  by  its  keeping  per- 
manently at  a  comparatively  high  temperature  the 
winds  which  pass  over  its  surface.  The  effect  of 
oceanic  currents  is  most  forcibly  shown  in  the  north- 
easterly projection  of  the  isothermal  curves  along  the 
coast  of  Northwestern  Europe.  These  (considering 
the  latitude)  abnormally  high  temperatures  in  Great 
Britain  are  doubtless  due  in  part  to  the  oceanic  circu- 
lation in  that  direction  ;  but  how  and  to  what  extent 
is  a  hotly  disputed  question.  Dr.  W.  B.  Carpenter 
maintained  that  this  amelioration  of  the  climate  of 
Northwestern  Europe  is  caused  by  the  general  oceanic 
circulation,  and  not  by  the  Gulf  Stream.  The  writer 
concurs  with  Dr.  Carpenter  in  believing  that  the  Gulf 
Stream,  as  such,  disappears  in  the  mid- Atlantic  Ocean, 
but  also  believes  that  not  enough  weight  has  been 
given  to  the  effect  of  the  quite  permanent  and  exten- 
sive barometric  depression  in  the  vicinity  of  Iceland, 
which  brings  in  its  circulatory  system  of  air  currents 
the  prevailing  southwest  winds,  most  essential  factors 
in  the  amelioration  of  British  climate.  It  is  signifi- 
cant that  any  marked  displacement  of  this  low  area  to 
the  southeast  results,  as  Buchan  has  plainly  shown,  in 
abnormally  low  temperatures  for  the  British  Isles, 
despite  the  Gulf  Stream  or  the  general  oceanic  cur- 
rents. Moreover,  it  is  an  even  question  if  the  unequal 
distribution  of  barometric  pressure,  with  its  attendant 
changes  above  referred  to,  are  not  quite  as  important 
factors  in  producing  the  general  oceanic  circulation 
as  is  the  vertical  distribution  of  temperature  set  forth 
by  Carpenter  as  the  predominating  influence. 

The  influence  of  mountains  upon  the  distribution  of 
temperature  depends,  in  part,  on  their  inducing  the 


AMERICAN  WEATHER. 


107 


served)  between  these  two  places  are  nearly  as  strik- 
ing in  their  variation,  being  61°  at  San  Francisco  and 


Annual  fluctuations  of  Temperature 


FIG.  19. 

128°  at  St.  Louis.  These  data  illustrate  in  the  most 
striking  manner  the  difference  between  a  continental 
climate  and  a  marine  climate  ;  for  the  peculiar  situ- 


108  AMERICAN  WEATHEB. 

ation  of  San  Francisco  upon  a  peninsula  causes  its 
climate  to  be  almost  insular. 

But  the  march  of  temperature  or  its  distribution 
throughout  the  year  is  of  the  greatest  importance,  and 
this  is  most  conveniently  illustrated  by  plotting  the 
monthly  means,  as  shown  in  Fig.  19.  This  variability 
of  temperature  throughout  the  year  has  an  absolute 
bearing  on  vegetation,  animal  life,  and  on  all  kindred 
phenomena  in  which  mankind  is  vitally  interested. 

The  amount  of  heat  received  by  any  place  on  the 
globe  (with  the  intervening  atmosphere  through  which 
the  sun' s  rays  pass)  depends  on  the  inclination  of  the 
solar  ray  and  the  length  of  the  day.  It  follows,  then, 
that  the  amount  of  heat  received  for  any  given  month 
depends  on  the  position  of  the  sun,  so  that,  as  Blan- 
f ord  has  set  forth,  the  greatest  quantity  of  solar  heat 
near  the  equinox  would  fall  at  the  equator,  between 
May  1st  and  August  15th  from  30°  and  40°  N.  latitude, 
and  for  the  six  weeks  nearest  the  solstice  at  the  North 
Pole.  The  character  of  the  surface — land  or  water, 
desert  or  forest — receiving  the  heat  tends  to  materially 
modify  the  march  of  temperature,  which  in  but  few 
locations  shows  these  theoretical  conditions. 

The  effect  of  the  greatest  insolation  is  evident  only 
on  lands  of  considerable  extent,  and  in  the  interior 
thereof.  In  "  Vade  Mecum,"  page  149,  Blanford  illus- 
trates the  temperature  conditions  of  India  by  a  chart 
for  May  (the  month  of  greatest  solar  heat  for  that 
country),  1875,  where  the  isotherms  are  concentric 
curves  following  the  contour  lines  of  the  peninsula, 
and  increasing  from  the  sea  until  they  exceed  95°  in 
the  interior. 

Fig.  19  contains  typical  illustrations  of  the  annual 
march  of  temperature  in  various  parts  of  the  Northern 
Hemisphere.  The  curve  for  Fort  Conger,  the  station 


Temperature 
for  January. 


AMEKICAN  WEATHER.  109 

having  the  lowest  known  mean  temperature  of  the 
globe  (—5°),  might  be  expected,  from  its  very  high  lati- 
tude, with  four  and  a  half  months  of  sunless  winter 
and  the  same  duration  of  continuous  summer  sunlight, 
to  show  more  forcibly  the  results  of  summer  insolation 
and  winter  radiation.  It  is,  however,  located  on  a 
land  of  limited  extent,  contiguous  to  enormous  ice- 
capped  lands  and  to  broad  straits  and  seas  which  fur- 
nish enough  aqueous  vapor  to  materially  modify  the 
march  of  temperature.  The  curves  of  Werchojansk, 
Siberia  (67°  K  lat.),  and  St.  Vincent,  Minn.  (49°  N. 
lat.),  illustrate  for  Asia  and  America,  respectively,  the 
extent  to  which  winter  radiation  can  chill  the  dry  air 
of  stations  situated  in  the  interior  of  great  continents, 
and  how  great  a  mean  temperature  summer  insolation 
induces  even  in  high  latitudes. 

St.  Louis,  Mo.,  and  Yuma,  Ariz.,  are  inland  sta- 
tions, while  New  York  City,  Jacksonville,  Fla.,  San 
Diego,  Cal.,  and  Yizagapatam,  India,  are  littoral  sta- 
tions, to  which  may  be  added  Massowah,  Red  Sea,  as 
it  is  so  near  to  the  mainland  as  to  feel  its  climatic  in- 
fluence. The  annual  curve  of  Singapore,  nearly  under 
the  equator,  illustrates  by  its  flatness  the  slight  vari- 
ability of  temperature  at  insular  stations  in  low  lati- 
tudes. 

On  Charts  Y.  and  YI.  the  temperature  conditions  of 
the  United  States  are  shown  by  the  isotherms  for  Jan- 
uary, the  coldest,  and  for  July,  the  warmest  months  of 
the  year.  It  is  to  be  noted  that  the  coldest  locality  is 
in  the  Red  River  Valley  and  the  adjacent  parts  of 
Manitoba,  the  temperature  decreasing  regularly  toward 
that  region  from  the  Gulf  of  Mexico,  the  Atlantic  and 
Pacific  oceans.  The  small  angle  at  which  the  rays  of 
the  winter  sun  reach  that  section,  the  length  of  the 
night  and  the  almost  total  absence  of  aqueous  vapor, 


t 
110  AMERICAN   WEATHER. 

form  conditions  which  reduce  insolation  and  facilitate 
to  a  marked  degree  nocturnal  radiation.  In  addition 
the  movement  eastward,  across  the  great  lakes,  of 
cylconic  storms,  results  in  drawing  southward  enor- 
mous masses  of  cold  air  from  Saskatchewan.  This 
movement  of  cold  air  is  facilitated  by  the  peculiar 
physical  features  of  the  country,  a  broad  valley  with 
gently  sloping  sides,  devoid  of  heavy  timber  and  un- 
broken by  highlands.  This  cold  of  translation  is 
nearly  always  intensified  by  rapid  nocturnal  radiation, 
so  that  in  this  section  occur  some  of  the  lowest  single 
temperatures  recorded  in  the  world. 

The  modification  of  temperatures  by  oceanic  influ- 
ences along  the  Atlantic  and  Gulf  coasts  during  Janu- 
ary is  quite  inconsiderable,  as  appears  from  Chart  Y. 
This  results  from  the  prevalent  direction  of  the  wind, 
which  is  from  the  northwest,  thus  superadding  in  most 
sections  east  of  the  Rocky  Mountains  the  cold  of 
translation  to  that  of  radiation. 

The  most  remarkable  feature  of  the  January  chart 
is  the  high  temperature  of  the  Pacific  coast  region. 
The  decrease  in  the  temperature  of  January  from 
Charleston,  on  the  Atlantic  coast,  to  Eastport  is  30° ; 
from  San  Diego,  Cal.,  to  Tatoosh  Island,  the  decrease  is 
only  12°,  which  is  but  slightly  greater  than  the  range 
in  the  temperature  of  the  surface  of  the  sea  between 
these  points. 

The  distribution  of  pressure  during  January  tends 
to  facilitate  this  equability  of  temperature.  During 
this  month  the  actual  pressure  over  California  is  in- 
creasing, while  in  Oregon  and  Nevada  it  is  decreasing, 
the  result  of  the  air  flowing  inward  from  the  higher 
area  over  the  Pacific.  The  circulation  of  prevailing 
winds  thus  induced  brings  westerly  winds  with  much 
aqueous  vapor,  almost  constant  cloudiness,  and  nearly 


AMERICAN   WEATHEK.  Ill 

continuous  rain  to  the  regions  north  of  California. 
The  prevailing  winds  in  Northern  California  are,  how- 
ever, northerly,  and  in  Southern  California  northeast- 
erly. However,  the  enclosed  valleys  of  the  Sacra- 
mento and  San  Joaquin,  the  Mohave  Desert,  and 
the  various  mountain  ranges  are  not  favorable  to 
steady  winds,  so  that  fortunately  many  interruptions 
occur  in  the  circulation,  and  westerly  winds  along  the 
coast  are  not  infrequent  in  Southern  California,  and 
quite  frequent  on  the  central  coast,  thus  bringing  large 
quantities  of  aqueous  vapor  which  is  locally  deposited, 
with  an  ameliorating  effect  on  the  temperature. 

Dr.  Haughton*  has  calculated  that  on  the  west 
coast  of  Ireland  the  heat  from  rainfall  is  equivalent  to 
half  that  from  the  sun. 

It  seems  to  the  author  that  the  rainfall  in  the  Pacific 
coast  region  very  largely  affects  the  mean  tempera- 
ture. It  is  significant  that  San  Diego,  with  its  7  inches 
of  winter  rain,  has  a  normal  seasonal  temperature  for 
its  latitude,  but  to  the  northward  the  precipitation  for 
the  winter  increases  to  14  inches  at  San  Francisco  and 
31  at  Tatoosh  Island,  with  a  similar  increase  in  ab- 
normally high  temperature  for  the  latitude,  the  excess 
at  Tatoosh  Island  being  nearly  10°. 

It  is  in  summer,  however,  that  the  effects  of  the  sea 
winds  are  most  evident  along  the  Pacific  coast,  as  will 
be  seen  by  reference  to  the  July  chart,  No.  VI. ,  of  mean 
temperatures.  Without  exception  the  coast  winds 
prevail  very  largely  from  the  west,  the  ocean  air  being 
drawn  inward  owing  to  the  high  temperature  and  con- 
sequently reduced  pressure  of  the  inland  valleys.  The 
gradient  is  so  gentle,  however,  that  the  aqueous  vapor 


*  Haughton  also  says  :  "  One  gallon  of  rainfall  gives  out  latent  heat 
sufficient  to  inelt  75  Jbs,  of  ice,  or  to  melt  45  Jbs,  of  cast  iron," 


112  AMERICAN   WEATHER. 

drawn  in  from  the  sea  is  taken  up  quickly  by  the  dry 
inland  air,  very  rarely  causing  condensation. 

The  enormous  differences  of  temperature  in  this 
region  are  unequalled  elsewhere.  From  67°  in  July 
at  San  Diego,  the  mean  temperature  rises  to  92°  at 
Yuma,  an  increase  of  25°  in  less  than  two  hundred 
miles.  The  contrasts  are  yet  more  striking  between 
Cape  Mendocino  and  Red  Bluff,  where,  in  less  than  one 
hundred  miles,  the  difference  amounts  to  28°. 

On  the  July  chart  (No.  VI.)  of  the  United  States  are 
two  illustrations  of  regions  heated  directly  by  the  sun, 
without  material  modifications  through  cloudiness, 
evaporation  of  rainfall,  or  transference  by  winds.  The 
sandy  soil,  with  scanty  vegetation,  the  absence  of  rain 
and  the  tranquil  atmospheric  conditions  in  the  lower 
Colorado  Yalley  and  adjacent  parts  of  California, 
Nevada,  and  Arizona,  are  followed  by  unusually  high 
summer  temperatures,  as  shown  by  the  closed  isotherms 
of  85°  and  90°.  Conditions  are  somewhat  less  favor- 
able in  the  Rio  Grande  Yalley,  which,  farther  to  the 
south,  also  has  closed  isotherms  of  85°  and  90°,  the 
former  being  present  from  the  middle  of  May.  These 
unusually  high  mean  temperatures  continue  in  both 
locations  until  about  the  autumnal  equinox. 

Elsewhere  in  July  the  isotherms  are  bent  materially 
southward  by  the  cooling  effects  of  the  great  lakes,  by 
sea  breezes  on  the  Atlantic  coast  from  Maine  to  North 
Carolina,  as  well  as  by  the  various  mountain  ranges. 

DIURNAL   MARCH. 

The  diurnal  march  of  temperature  depends  directly 
upon  the  sun's  rays,  so  that  the  maximum  and  mini- 
mum phases  principally  depend  upon  the  absence  of 
clouds  and  the  length  of  the  day  and  duration  of  sun- 
shine. As  a  rule,  the  daily  maximum  temperature  oc- 


AMERICAN  WEATHEK. 


113 


curs  from  2  to  4  P.M.,  although  in  regions  where  the  air 
is  very  dry,  or  the  effect  of  the  sun's  rays  very  small, 
it  may  occur  before  2  P.M.  The  daily  minimum  occurs 
generally  about  dawn,  at  that  hour  when  the  effect  of 
the  terrestrial  radiation  is  counteracted  by  reflected 
heat  from  the  upper  strata  of  the  atmosphere  from  the 
morning  sun.  In  winter  the  minimum  has  a  tendency 


Dally  Fluctuation  of  Temperature. 

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to  occur  slightly  before  dawn,  while  in  summer  it  is 
somewhat  delayed. 

Purely  local  causes,  such  as  the  influence  of  sea 
breezes  or  the  recurrence  of  rain,  tend  to  change  the 
hour  of  the  maximum,  especially  in  low  latitudes. 

The  diurnal  march  of  temperature  is  illustrated  by 
Fig.  20,  which  shows  the  diurnal  changes  at  various 
stations.  The  data  is  for  the  entire  year,  except  at 


114  AMERICAN   WEATHER. 

Fort  Conger,  where  temperatures  for  the  long  Arctic 
winter  are  used  in  order  to  show  that  the  absence  of 
the  sun  causes  the  maximum  and  minimum  to  occur 
accidentally  at  various  hours. 

On  Chart  No.  IX.  is  shown  the  length  of  continuance 
of  daily  mean  temperatures  above  50°  Fahr.  These 
data  indicate  in  a  marked  degree  the  climatic  charac- 
ter, as  regards  temperature,  of  the  United  States  ;  since 
the  daily  mean  temperature  of  50°  is  not  only  about 
the  lowest  mankind  in  general  deem  comfortable,  but 
is  also  a  critical  point  as  regards  the  growth  and  de- 
velopment of  the  most  important  staple  crops  of  the 
United  States.  The  southwestern  part  of  California, 
the  greater  part  of  Florida,  and  the  immediate  Gulf 
coast  are  the  only  portions  of  the  country  where  the 
temperature  continues  above  50°  throughout  the  entire 
year.  The  entire  country  south  of  the  35th  parallel, 
and  such  portions  of  California  as  are  to  the  north- 
ward, are  favored  for  eight  months  in  the  year  with 
such  temperatures,  while  even  the  most  northern  parts 
of  the  country  between  the  45th  and  49th  parallels, 
from  Maine  to  Montana,  have  nearly  five  months  of 
these  temperatures. 

Chart  No.  X.  shows  the  continuance  of  the  daily 
mean  temperatures  of  the  United  States  below  32° 
Fahr.,  and  thus  shows  at  a  glance  the  comparative 
severity  of  the  winter  for  the  different  portions  of  the 
country. 

The  Pacific  coast  region  for  two  hundred  miles  in- 
land is  free  from  any  daily  mean  temperatures  (except 
on  very  rare  occasions)  below  32°.  Similarly  favorable 
conditions  exist  to  the  southward  of  the  38th  parallel 
over  the  country  east  of  the  Mississippi  River  and 
south  of  the  35th  parallel  to  the  westward.  Between 
the  45th  and  49th  parallels  of  north  latitude,  and 


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AMERICAN   WEATHER.  115 

from  Montana  eastward  to  Northern  Maine,  the  sever- 
ity of  the  weather  in  winter  is  shown  by  the  fact  that 
the  average  daily  temperature  is  below  32°  for  periods 
averaging  from  four  to  five  and  a  half  months,  the 
longest  continuance  of  such  temperature  being  in  the 
valley  of  the  Red  River  of  the  North,  the  station  at 
St.  Vincent,  Minn.,  having  on  an  average  five  and  a  half 
months'  daily  temperatures  below  the  melting  point  of 
ice.  The  same  station  also  has  the  least  number  of 
days  of  mean  temperature  above  50°,  — 133  days  an- 
nually. 

The  months  of  January  and  July  have  been  selected 
as  representative  months,  since  they  are,  as  a  rule,  for 
the  Northern  Hemisphere  the  coldest  and  warmest 
months,  respectively,  of  the  year. 

In  the  United  States  the  greatest  mean  obtains  in 
July  as  a  whole.  As  a  marked  exception  the  month  of 
August  is  warmer  along  the  immediate  Pacific  coast, 
from  San  Diego,  CaL,  to  Sitka,  Alaska.  From  local 
causes  San  Francisco  does  not  attain  its  maximum 
monthly  heat  until  September.  The  lowest  monthly 
temperature  in  the  United  States  falls  in  January,  ex- 
cept in  Alaska  and  the  Aleutian  Islands,  where  it  ob- 
tains in  February. 

In  some  portions  of  the  globe,  generally  between  the 
equator  and  thirty  degrees  north  latitude,  the  month 
of  June  is  slightly  warmer  than  that  of  July  ;  this  is 
especially  true  of  India,  owing  to  the  rainy  season  set- 
ting in.  The  highest  monthly  mean  temperatures  of 
the  Northern  Hemisphere  occur,  nevertheless,  in  May 
and  in  India,  as  is  indicated  by  the  following  data  : 

Mooltan,  Indus  Valley,  30.2°  N.,  71.5°  E.,  420  feet 
elevation  (15  years),  93.9°  ;  Agra,  inland,  27.2°  N., 
78°  E.,  555  feet  elevation  (22  years),  94.5°  ;  Bickaneer, 
28°  N.,  73°  E.,  744  feet  elevation  (8  years),  95.0°; 


116  AMERICAN  WEATHER. 

Jacobabad,  Indus  Valley,  28.4°  K,  68°  E.,  185  feet 
elevation  (8  years),  95.9°,  the  extreme  of  high,  monthly 
temperatures. 

At  Vizagapatam,  on  Bay  of  Bengal,  17.7°  N.,  83.4° 
E.,  31  feet  elevation  (16  years),  the  annual  tempera- 
ture is  82.8°.  This  is  only  exceeded  by  the  records  of 
Massowah,  an  island  in  the  Red  Sea,  where  the  annual 
temperature,  dependent  on  a  record  of  a  few  years, 
however,  is  the  highest,  perhaps,  in  the  world.  The 
highest  annual  and  monthly  temperatures  in  the 
United  States  are  those  of  Yuma,  Ariz.,  32.8°  N., 
114.5°  W.  (12  years),  annual,  72.1°,  July,  92.0°  ;  Fort 
Mojave,  Ariz.  (8  years),  annual,  72.7°,  July,  94.9° ; 
Rio  Grande  City,  Tex.  (7  years),  annual,  73.1°,  June, 
93.9°. 

The  absolute  maximum  for  a  single  month  in  the 
United  States  is  that  for  July,  1882,  97.3°,  at  Eio 
Grande  City,  Tex.  The  lowest  mean  temperatures  in 
the  United  States  are  at  St.  Vincent,  Minn.  (10  years), 
annual,  34° ;  January,  4.8°.  The  absolute  lowest  mean 
monthly  temperature  (13.4°)  occurred  at  this  station, 
January,  1883. 

INTERRUPTIONS  OF  TEMPERATURE. 

The  increase  of  temperature  from  January  to  July 
and  the  decrease  during  the  rest  of  the  year  do  not 
occur  with  absolute  and  unbroken  regularity.  Every 
storm  which  passes  across  the  United  States  affects  for 
the  time  being  the  normal  march  of  temperature,  and 
replaces  the  gradual  and  almost  imperceptible  seasonal 
changes  by  the  more  sudden  and  violent  accidental 
fluctuations.  As  will  be  seen  later,  in  treating  of 
storms  and  cold  waves,  these  accidental  variations  of 
temperature  last  about  three  days  only.  The  recur- 


AMERICAN   WEATHER. 


117 


rences  of  the  most  marked  of  these  accidental  changes, 
year  after  year,  are  so  marked  that  they  have  im- 
pressed themselves  on  the  public  mind.  The  warm 
days  of  the  early  year  known  in  New  England  as  the 


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FIG.  21. 


"  January  thaw,"  the  cold  days  of  April,  called  by 
the  Scotch  "  Borrowing  Days,"  and  the  "  cold  days 
of  May"  are  the  best  and  most  widely  known  of  these 
interruptions. 


118  AMERICAN   WEATHER. 

The  cold  days  of  May,  being  common  to  both  Europe 
and  America,  thus  merit  examination.  Their  appear- 
ance in  Scotland  is  placed  by  Buchan  from  May  9th 
to  14th,  while  in  America  they  are  supposed  to  occur 
from  May  10th  to  15th. 

In  Fig.  21  are  charted  the  normal  mean  temperatures 
for  each  day  of  May  for  Omaha,  Neb.  ;  Chicago,  111.  ; 
Toledo,  O.  ;  Buffalo  and  Oswego,  IS".  Y.  ;  Philadelphia, 
Pa.,  and  Lynchburg,  Ya.  These  means  have  been 
calculated  from  observations  varying  from  fourteen  to 
sixteen  years.  It  will  be  noticed  that  the  interruptions 
of  temperature  between  May  5th  and  25th  are  marked 
and  persistent.  Two  peculiarities  appear,  however— 
viz.  : 

1st.  That  if  a  straight  line  be  drawn  cutting  the 
mean  temperature  of  both  the  first  and  last  day  of  the 
month  at  each  station,  the  greatest  departures  from  the 
line  are  the  high  temperatures  from  May  17th  to  22d, 
so  that  the  marked  feature  in  the  United  States  is 
rather  the  warm  than  the  cold  days  of  May. 

2d.  That  the  phases  of  heat  and  cold,  more  especially 
the  latter,  apparently  pass  from  northwest  to  south- 
east, as  they  occur  first  at  the  more  westerly  or  north- 
erly stations. 

It  further  appears  that  these  marked  departures  do 
not  obtain  in  the  St.  Lawrence  Valley,  in  New  Eng- 
land, to  the  south  of  the  35th  parallel,  nor  to  the  west- 
ward of  the  Missouri  Valley. 

A  detailed  examination  proves  conclusively  that  these 
interruptions  of  temperature  arise  from  the  passage  of 
low  area  storms  from  west  to  east,  which  induce  abnor- 
mally high  temperatures,  to  be  followed  later  by  high 
areas  in  the  rear.  These  high  areas,  drawing  south- 
eastward the  dry  cold  air  from  British  America,  pro- 
duce the  sudden  and  abnormal  falls  of  temperature 


AMERICAN   WEATHER.  119 

known  popularly  as  "cold  waves."  As  Buchan  said, 
twenty  years  since,  interruptions  of  temperature  de- 
pend on  differences  of  atmospheric  pressure,  which  in- 
duce either  equatorial  or  polar  currents,  according  to 
the  relative  position  of  the  storm  centre. 

It  is  evident  from  an  examination  of  weather  con- 
ditions attendant  on  warm  days  in  the  northern  parts  of 
the  United  States  during  January,  that  they  result  from 
the  movement  of  low-area  storms  eastward,  in  paths 
of  unusually  high  latitudes,  thus  inducing  southerly 
winds  for  a  few  days  over  the  regions  favored  by  ab- 
normally high  temperatures. 

As  will  appear  later  in  this  work,  there  is  no  suffi- 
cient reason  to  support  a  belief  in  recurring  cycles,  for 
any  locality,  of  excessive  or  deficient  phases  of  rain- 
fall, or  indeed  of  temperature,  although  one  may  ad- 
mit that  the  amount  of  solar  heat  for  the  whole  world 
may  be  greater  in  the  year  of  minima  sun  spots  than  in 
the  maxima. 


CHAPTER  X. 

RANGES,    VARIABILITY,    AND    EXTREMES    OF   TEMPERA- 
TURE. 

ONE  of  the  most  important  elements  of  any  climate 
is  its  range  of  temperature,  which,  marks  it  as  conti- 
nental or  marine. 

The  marked  feature  of  continental  climate  is  the 
great  difference  between  its  extreme  temperatures, 
whether  of  day,  month,  or  year.  The  greatest  differ- 
ences occur  in  the  interior  of  continents,  where  the 
small  amount  of  aqueous  vapor  in  the  air  permits  rapid 
radiation  in  winter  and  a  high  degree  of  insolation 
in  summer.  These  differences  may  be  called  extreme 
in  North  America,  where  they  almost  equal  the  exces- 
sive ranges  of  Central  Asia. 

On  the  contrary,  a  marine  climate  is  characterized  by 
small  ranges  and  a  general  freedom  from  violent 
changes.  The  annual  fluctuation  in  the  monthly  mean 
at  Singapore,  a  tropical  marine  station  (Fig.  19),  is  only 
3.7°.  In  the  United  States  may  be  instanced  Tatoosh 
Island,  San  Francisco,  and  San  Diego,  characteristic 
marine  stations  of  the  Pacific  coast,  with  differences 
between  the  hottest  and  coldest  months  of  8°,  9°,  and 
15°  respectively.  The  continental  stations  of  Wer- 
chojansk,  Siberia,'  and  Saint  Vincent,  Minn.,  have 
differences  between  similar  months  of  120.4°  and  70.7° 
respectively. 

The  difference  between  extreme  temperatures  at  a 
station  is  called  the  range,  and  is  annual,  monthly,  or 


jdmuinTemperatures 

ever  oLserved 


AMERICAN   WEATHER.  121 

daily,  according  as  the  observations  referred  to  are  for 
a  day,  month,  or  year.  When  the  range  is  obtained 
from  the  entire  known  series  of  observations,  it  is 
termed  the  absolute  range,  and  the  maxima  and  minima 
similarly  determined  are  also  termed  absolute. 

The  absolute  range  of  the  Northern  Hemisphere,  and 
doubtless  of  the  world,  is  217.8°,  depending  on  the  ab- 
solute maximum  of  127.4°  at  Ouargla,  Algeria,  July 
17th,  1879,  and  the  absolute  minimum  of  — 90.4°  at 
Werchojansk,  Siberia,  January  15th,  1885. 

It  was  once  questioned  if  the  human  body  could  un- 
dergo unharmed  such  enormous  temperature  changes, 
and  the  question  is  now  answered  in  the  affirmative, 
although  j)robably  no  person  has  ever  experienced  the 
entire  range.  The  author,  however,  has  closely  ap- 
proximated it,  having  experienced  at  Fort  Conger,  Feb- 
ruary, 1882,  the  very  low  temperature  of  — 66.2°,  and  on 
the  Maricopa  Desert,  Ariz.,  August  28th,  1877,  saw  the 
temperature  of  the  air  at  114°,  while  the  metal  of  his 
Aneroid  barometer,  beside  him  as  he  rode,  assumed  a 
steady  temperature  of  144°. 

The  enormous  absolute  ranges  of  Northern  Montana, 
from  150°  to  170°,  have  been  experienced  by  many 
thousands  without  apparent  injury,  as  evidenced  by  the 
unusual  health  and  robustness  of  the  inhabitants  of 
that  Territory. 

The  absolute  ranges,  as  a  rule,  exceed  the  annual 
slightly ;  so  that  the  former  is  fairly  indicative  of  both. 

The  absolute  ranges  of  temperature  in  the  United 
States  are  exceedingly  large  as  compared  with  Europe, 
and  indeed  are  equalled  nowhere  in  the  world  except 
possibly  in  Northern  Asia.  The  smallest  absolute 
ranges  pertain  to  the  immediate  Pacific  coast,  being 
least  (60°)  at  San  Francisco,  and  increasing  slightly, 
both  to  the  northward  and  southward,  to  61°  at  Ta- 


122  AMERICAN  WEATHER. 

toosh  Island  and  69°  at  San  Diego.  Except  a  narrow 
fringe  of  land  along  the  Pacific  Ocean  and  a  similar 
narrow  fringe  along  the  South  Atlantic  and  Gulf  coasts, 
the  absolute  range  of  temperature  everywhere  exceeds 
100°;  the  range  increasing  rapidly  as  one  goes  inland, 
and,  as  a  rule,  decidedly  so  with  elevation  and  latitude 
— i.e.,  with  the  lessening  thickness  of  the  superin- 
cumbent strata  of  the  atmosphere,  and  the  increasing 
dryness  of  the  air.  Ranges  exceeding  120°  have 
occurred  over  a  great  part  of  the  Ohio  Valley,  the 
whole  Upper  Mississippi  and  Missouri  valleys,  and  the 
northern  half  of  the  Rocky  Mountain  and  plateau 
regions.  The  ranges  exceed  140°  for  all  Dakota  and 
Montana ;  and  in  the  latter  Territory  the  maximum 
absolute  ranges  of  the  United  States  have  been  ex- 
perienced—namely, 169.8°  at  Fort  Benton  and  172.7° 
at  Poplar  River. 

The  absolute  ranges  for  any  place  in  the  United 
States  may  be  approximately  determined  from  Charts 
VII.  and  VIII.,  which  show  the  absolute  maximum  and 
minimum  temperatures  for  the  whole  country. 

The  greatest  absolute  ranges  of  the  globe  are  those 
recorded  in  the  interior  of  Siberia,  where  the  variations 
in  temperature  somewhat  exceed  those  of  Montana. 
The  extreme  ranges  are  Yeniseisk,  169°  ;  Banschikowo 
(62°  K,  132°  E.),  175°  ;  Werchojansk(67.5°  K,  134°  E.), 
178°  ;  and  Yakutsk,  181.4°  ;  the  last  doubtless  the 
greatest  in  the  world. 

In  India  absolute  ranges  of  temperature  rarely  equal 
100° ;  the  greatest  in  the  Punjab.  The  absolute  range 
at  Galle,  on  the  coast  of  Ceylon,  is  but  24.4°  from  92.0° 
to  68.6°  ;  for  the  year  1875  it  was  16.2°.  At  ISTan- 
cowry,  Bay  Islands,  the  annual  range  in  1879  was  17.8°. 
In  no  year  does  it  exceed  19°.  In  Algeria  absolute 
ranges  exceeding  100°  are  not  usual,  except  along  the 


AMERICAN   WEATHER.  123 

edge  of  Sahara.  At  Bon  Saada,  35°  N.,  however,  an 
annual  range  of  128.8°  has  been  observed. 

The  absolute  -range  of  annual  temperature  is  to  a 
considerable  extent  dependent  on  locality,  appearing  to 
increase  with  latitude  and  with  distance  from  the  sea. 
It  rarely  exceeds  8°  in  the  United  States,  and  according 
to  Loomis,  amounted  to  only  6.3°  in  eighty-six  years  at 
New  Haven,  Conn.,  a  sea-coast  station.  At  Bismarck, 
Dak.,  however,  it  amounted  to  9.3°  in  nine  years. 

Extreme  monthly  ranges  of  or  exceeding  100°  are 
occasionally  observed  in  Montana,  Dakota,  and  Ne- 
braska, while  along  the  Atlantic  seaboard  ranges  ex- 
ceeding 70°  are  unknown,  and  on  the  Pacific  coast 
barely  equal  55°.  Fort  Ben  ton,  Mon.,  has  reported  the 
greatest  monthly  range  in  the  United  States,  117°,  from 
58°  on  December  12th,  1880,  to  —59°  on  the  29th.  The 
greatest  range  at  Tatoosh  Island,  Wash.  Ter.,  in  any 
month  is  but  41.4°,  while  Key  West  has  had  a  range 
of  46°.  At  San  Francisco,  Cal.,  the  range  for  January, 
1884,  was  16°.  Galle,  Ceylon,  in  July,  1877,  had  a 
range  of  7.1°,  and  at  Paramaribo,  South  America,  the 
range  in  October,  1878,  was  only  7.0°,  perhaps  the 
smallest  ever  recorded  at  any  place. 

Of  more  vital  importance  than  absolute  or  monthly 
range  is  the  daily  range,  since  violent  or  extreme 
changes  of  temperature  within  a  few  hours  are  harm- 
ful to  vegetable  and  animal  life  and  growth. 

Over  the  United  States,  from  the  Mississippi  Valley 
eastward,  the  mean  daily  range  varies  throughout  the 
different  months  of  the  year  from  12°  to  20°.  The  daily 
range  from  the  Missouri  Valley  and  Texas  westward, 
except  along  the  Pacific  coast  line,  varies  from  20°  to 
35°.  The  only  portion  of  the  country  favored  by  very 
small  daily  ranges  is  that  portion  of  the  Pacific  coast 
situated  on  or  within  a  hundred  miles  of  the  Pacific 


124  AMERICAN   WEATHEK. 

Ocean.  The  highest  daily  ranges  occur,  as  a  rule,  in 
the  summer  months,  from  May  to  July,  inclusive,  ex- 
cept along  the  South  Atlantic  and  Gulf  coasts,  where 
the  greatest  daily  ranges  occur  in  the  winter  months — 
December  or  January.  The  mean  daily  ranges  are 
least  in  December  and  January,  except  in  Texas,  along 
the  Gulf  and  South  Atlantic  coasts,  where  they  gener- 
ally attain  the  minimum  in  September.  There  are  local 
departures  from  these  general  rules,  usually  caused  by 
the  prevailing  wind  shifting  to  or  from  the  sea,  or  by 
the  intervention  of  cloud  and  rain.  In  these  cases  the 
aqueous  vapor  plays  a  very  important  part  in  modify- 
ing the  ranges,  which  otherwise  would  often  .be  ex- 
treme. 

Fig.  22  contains  typical  curves  showing  the  annual 
fluctuation  of  the  mean  daily  ranges  at  selected  stations 
in  the  United  States. 

The  daily  ranges  over  the  Rocky  Mountain  and 
plateau  regions  are  extraordinary,  and  it  is  evident 
that  Buchan,  when  writing  of  the  great  range  of  41.3° 
at  Pachbudra,  India,  during  a  single  month — March, 
1880 — was  unaware  of  the  extraordinary  daily  fluctua- 
tions of  the  temperature  in  Arizona  and  Southern  Cali- 
fornia. At  Fort  Apache,  Ariz,  (elevation,  5050  feet),  the 
mean  daily  range  for  June  is  no  less  than  42.6°.  These 
figures  are  not  greatly  in  excess  of  the  ranges  at  Pres- 
cott  (elevation,  5340  feet)  and  Fort  Grant,  Ariz,  (eleva- 
tion, 4860  feet),  at  which  places  the  average  daily  range 
for  the  same  months  is  36°.  Even  as  remarkable  as  are 
these  ranges  they  are  exceeded  at  Campo,  Cal.  (eleva- 
tion, 2710  feet),  where  the  mean  range  for  September  is 
45.4°,  and  from  June  to  October,  inclusive,  averages 
44. 8°.  Average  daily  ranges  during  single  months  have 
somewhat  exceeded  these  amounts.  At  Fort  Apache, 
in  June,  1888,  the  daily  range  averaged  45. 7°  ;  Phoenix, 


AMERICAN  WEATPIEK. 


FIG.  22. 

Ariz.,  June,  1879,  48 A°  ;  Campo,  CaL,  September,  1880, 
48.8°,  June,  1881,  49.0°,  and  in  June,  1880,  the  mean 
daily  range  was  50.6°. 

Among  stations  having  small  daily  ranges  for  a  single 
month  may  be  selected  Key  West,  Fla.,  December, 
1877,  6.6°  ;  San  Francisco,  CaL,  December,  1881,  6.5°, 
and  Fort  Canby,  Wash.  Terr.,  December,  1885,  6.1°. 


126  AMERICAN   WEATHEE. 

The  stories  are  many  in  Texas  of  100°  at  noon  and 
ice  at  night,  and  while  all  such  tales  may  be  dismissed 
as  apocryphal,  yet  they  rest  on  better  foundation  than 
many  others  less  startling. 

As  might  reasonably  be  expected,  the  greater  part 
of  extreme  and  sudden  changes  of  temperature  occur 
in  Dakota,  Minnesota,  and  Montana.  It  is  not  a  cold 
of  radiation,  but  is  almost  entirely  of  translation,  owing 
to  the  intensely  cold,  dry  air  flowing  out  of  British 
America.  The  following  are  the  most  remarkable 
changes  from  this  cause  in  24  hours  :  Fort  Maginnis, 
Mon.,  January  6th,  1886,  a  fall  of  56.4°,  49.7°  of  it  in 
8  hours  ;  Helena,  Mon.,  January  6th,  1886,  55.0°,  50.6° 
of  it  in  16  hours  ;  Dead  wood,  Dak.,  January  21st,  1886, 
a  fall  of  55.3°,  of  which  46.2°  in  8  hours  and  54.2°  in  16 
hours  ;  Denver,  Col.,  December  27th,  1886,  a  fall  of 
60.4°,  34.3°  of  it  in  8  hours  ;  Lamar,  Mo.,  February  llth, 
1887,  a  fall  of  60.3°,  58.5°  of  it  in  9  hours  ;  Abilene, 
Tex.,  December  27th,  1886,  a  fall  of  63.3°  in  16  hours. 

In  Arizona,  California,  Nevada,  Utah,  and  Texas 
very  remarkable  changes  occur  in  the  dry,  elevated 
regions,  where  the  morning  minimum,  slightly  above 
the  freezing-point,  occasionally  rises  from  40°  to  60°  by 
noon  or  shortly  after.  At  Denver,  Col.,  November 
27th,  1886,  the  temperature  rose  47.3°  in  8  hours,  and 
on  January  19th,  1886,  it  rose  53°  in  16  hours ;  Las 
Animas,  Cal.,  February  5th,  1887,  there  was  a  rise  of 
58°,  and  February  27th,  1887,  a  rise  of  55°,  52°  of  it  in 
8  hours ;  Fort  Apache,  Ariz.,  six  rises  took  place  in 
June,  1886,  of  50°,  of  which  four  cases  occurred  in  8 
hours,  the  greatest,  55.9°,  in  24  hours,  and  50.6°  in  8 
hours ;  Campo,  Cal.,  June  23d,  1882,  59°  rise,  55.1°  in 
8  hours,  and  Florence,  Ariz.,  June  22d,  1881,  65°  rise, 
50°  in  8  hours.  This  last  instance  is  the  greatest  daily 
variation  as  far  as  known.  Its  accuracy  is  confirmed 


AMERICAN   WEATHER.  127 

by  other  extreme  ranges  in  Arizona  on  that  day,  no- 
tably by  a  rise  at  Tucson  of  54°,  44°  of  it  in  8  hours. 

In  Thibet  it  is  said  the  temperature  has  been  known 
to  fall  90°  from  (20°  C.,  68°  P.,  to  —30°  C.,  —22°  F.)  in 
about  15  hours,  from  the  mid-day  maximum  to  morn- 
ing minimum.  This  statement  may  reasonably  be 
questioned  in  view  of  the  ranges  given  above,  and  also 
since  at  Leh,  Ladak,  a  dry  elevated  station  west  of 
Thibet,  the  range  of  any  month  does  not  exceed  60°, 
and  of  the  year  is  but  91.4°. 

MAXIMUM   AND   MINIMUM   TEMPERATURES. 

According  to  Mr.  S.  A.  Hill,  Meteorological  Reporter 
for  Central  India,  amateur  observers  in  Australia  occa- 
sionally are  in  rivalry  as  to  who  can  obtain  the  highest 
readings.  All  meteorologists  who  have  discussed  mis- 
cellaneous data  have  had  occasion  to  question  the  ac- 
curacy of  extreme  thermometer  readings. 

Statements  regarding  extreme  temperatures  must  al- 
ways be  received  with  more  or  less  caution,  owing  not 
only  to  the  imperfection  and  incorrectness  of  ther- 
mometers, but  also  on  account  of  unsuitable  exposure. 
Within  the  past  eighteen  years  much  attention  has 
been  given  to  these  points,  and  consequently  readings 
from  the  different  weather  services  may  be  received 
with  a  greater  degree  of  credibility  than  previously  ob- 
tained. The  highest  temperatures  of  the  world  occur 
over  the  desert  of  Sahara,  the  plains  of  India,  in  the 
interior  of  Australia,  and  in  the  valleys  of  the  Gila 
and  Southern  Colorado  in  America. 

With  regard  to  maximum  temperatures  from  the 
Sahara  there  is  no  definite  information,  but  we  have 
the  most  carefully  made  and  reliable  readings  from  the 
Algerian  system,  at  the  stations  of  which  the  simoom 
blows  from  the  Sahara.  It  appears,  however,  that  tern- 


128  AMERICAN  WEATHER. 

peratures  exceeding  120°  F.  are  unusually  rare.  At 
Orleans ville,  on  July  21st  and  August  21st,  1881,  a 
temperature  of  120.6°  was  observed,  and  in  July,  1880, 
at  Tizi  Ouzon,  Algeria,  a  temperature  of  121.1°.  On 
July  17th,  1879,  at  Aumale,  Algeria,  the  very  extraor- 
dinary temperature  of  125.6°  was  registered,  and  on 
August  27th,  1884,  at  Ouargla,  32°  K,  5°  E.,  on  the 
northern  edge  of  the  African  desert,  the  temperature 
of  the  air  rose  to  127.4°,  probably  the  highest  registered 
by  a  trained  observer  from  a  reliable,  well-exposed 
thermometer. 

It  would  seem  that  very  high  temperatures  are  equally 
rare  in  India,  which  country  has  constantly  been  cred- 
ited with  extraordinary  temperatures  of  130°  and 
higher.  In  ten  years  (1875-84)  only  the  following 
temperatures  exceeding  120°  were  registered  :  Agra  and 
Lahore,  120.3°  ;  Jacobabad,  120.9°,  Sialkot,  and  Dera 
Ismail  Khan,  32°  N.,  71°  E.,  125°,  June,  1875. 

On  Charts  VII.  and  VIII.  appear  isotherms  of  the 
highest  and  lowest  temperatures  ever  recorded  in  the 
United  States.  The  charts  are  based  primarily  on  ob- 
servations of  the  United  States  Signal  Service,  owing 
to  the  uniformity  of  exposure  and  the  fact  that  correc- 
tions have  been  made  for  the  very  common  errors, 
especially  in  low  readings.  It  will  be  noticed  that  a 
considerable  uniformity,  without  regard  to  latitude,  ap- 
pears in  the  highest  temperatures,  which  practically 
range  from  100°  to  110°.  Temperatures  higher  than 
100°  have  occurred  in  all  sections  except  along  the  im- 
mediate Pacific  coast,  in  the  region  of  the  great  lakes, 
over  the  Blue  Ridge,  Allegheny,  and  the  high  portions 
of  the  Rocky  Mountain  ranges  and  at  certain  stations 
on  the  New  Jersey  and  New  England  coasts.  The 
maximum  temperature  at  Tatoosh  Island  is  the  lowest 
in  the  country  (75°),  but  the  series  of  years  is  very 


ImumTeinperatures 

ever  observed 


AMERICAN   WEATHEK.  129 

short.  The  lowest  maximum  from  a  series  of  fifteen 
years  is  that  of  Eastport,  Me.,  88°.  Temperatures  ex- 
ceeding 110°  have  occurred  in  the  Valley  of  the  Rio 
Grande,  the  southern  portions  of  New  Mexico,  Ari- 
zona, and  the  extreme  southeastern  part  of  California. 

No  temperature  observed  at  any  Signal  Service  sta- 
tion has  ever  reached  120°.  The  highest  recorded  read- 
ings have  been  119°  at  Fort  McDowell  and  Phoenix, 
Ariz.,  June,  1883,  and  118°  at  Yuma,  Ariz.,  July,  1878. 
From  other  observations  are  quoted  temperatures  of 
128°  at  Mammoth  Tank,  Cal.,  July,  1887;  122°  at 
Humboldt,  Cal.,  July,  1887;  121°  at  Fort  Miller,  Cal., 
June,  1853  ;  Fort  Boise,  Ida.,  August,  1871  ;  120°  at 
Fort  McRae,  N.  M.,  June,  1873  ;  119°  at  Fort  Mojave, 
Ariz.,  August,  1875,  June,  1876,  and  July,  1877  ;  Fort 
Yuma,  Cal.,  July,  1877 ;  Fort  Miller,  Cal.,  July,  1853. 
The  highest  temperatures  ever  recorded  in  the  various 
States  and  Territories  are  to  be  found  in  table  No.  7. 

The  lines  of  lowest  temperatures  are  much  more  reg- 
ular. The  only  portions  of  the  country  where  the 
temperature  does  not  sink  below  zero,  Fahrenheit,  are 
California,  Arizona,  the  immediate  coasts  of  Oregon, 
Washington  Territory,  and  Delaware,  and  about  200 
miles  inland  along  the  South  Atlantic  and  Gulf  coasts. 
The  considerable  elevation,  high  latitude,  and  great 
dryness  of  the  air  in  Northern  Montana  favor  nocturnal 
radiation  into  space,  and  thus  cause  some  of  the  lowest 
temperatures  known  on  the  face  of  the  globe. 

The  temperature  of  space,  or,  as  it  is  known,  the  ab- 
solute zero,  is  placed  at  — 493°  F.,  so  that  there  is  an 
enormous  margin  between  the  temperature  of  inter- 
planetary space  and  the  lowest  recorded  temperature 
of  the  world,  —90°  at  Werchojansk. 

The  impression  is  general  that  temperatures  of  forty 
degrees  below  zero  are  not  uncommon  in  the  United 


130  AMERICAN  WEATHER. 

States.  Such  is  not  the  fact,  as,  except  on  the  summit 
of  Mount  Washington,  this  degree  of  cold  has  been 
reported  only  from  the  following  Signal  Service  stations 
in  Dakota,  Northern  Minnesota,  and  Northern  Mon- 
tana. Montana:  Poplar  River,  — 63.1°  (January  1st, 
1885)  ;  Fort  Benton,  —59°  (December) ;  Fort  Assini- 
boine,  —55.4°  (February)  ;  Fort  Ouster,  —47.5°  (De- 
cember) ;  Fort  Shaw,  —44.5°  (December) ;  FortMagin- 
nis,  — 42.0°  (February);  Helena,  —40.5°;  Dakota: 
FortBuford,  — 48.2°  ;  Bismarck,  —43.6°  ;  FortTotten, 
-43°  ;  Huron,  —42.8°  ;  Fort  Yates,  —41.0°  ;  Minne- 
sota :  Moorhead,  — 47.5° ;  St.  Vincent,  — 51°  (Decem- 
ber, 1873).  Unless  otherwise  noted,  the  readings  oc- 
curred in  January. 

On  the  summit  of  Mount  Washington  the  tempera- 
ture of  — 50°  has  been  observed  on  Pike's  Peak,  — 39.1. 

Other  instances  of  temperatures  forty  degrees  below 
zero  have  been  recorded,  many  being  most  doubtful 
readings,  while  others  are  probably  a  few  degrees  in 
error,  owing  to  the  fact  that  the  instruments  have  not 
been  tested  for  low  temperatures. 

The  following  are  the  most  reliable  : 

Colorado :  Fort  Garland,  —40°  (1873) ;  Dakota  : 
Webster,  —44°  (1887);  Fort  Randall,  —44°  (1875); 
Iowa :  Tail,  —40°  (1881) ;  Humboldt,  —42°  (1885)  ; 
Michigan :  Fort  Brady,  — 47°  (1873) ;  Minnesota  : 
Fort  Ripley,  —44°  (1860)  ;  Fort  Ripley  —43°  (1863) ; 
Northfield,  —41°  (1885)  ;  Montana :  Fort  Ellis,  —53 
(1872)  ;  Vermont :  Port  Mills,  —42°  (1887)  ;  Lunen- 
burg,  —45°  (1872)  ;  Randolph,  —40°  (1872)  ;  Wiscon- 
sin :  Embarras,  —40°  (1875) ;  Neillsville,  —42°  (1885) ; 
Fond  du  Lac,  —42°  (1887) ;  Wyoming  :  Fort  Laramie, 
—40°  (1864). 

Central  Siberia  presents  most  favorable  conditions 
for  very  low  temperatures,  elsewhere  unequalled. 


AMERICAN  WEATHER.  131 

The  lowest  monthly  mean  temperatures,  as  well  as 
the  lowest  single  temperatures  in  the  world,  have  been 
noted  at  Werchojansk,  Siberia,  67.5°  K,  134°  E.,at 
which  place,  on  January  15th,  1885,  the  remarkably  low 
temperature  of  — 90.4°  was  observed,  and  the  average 
temperature  for  the  month  was  — 63.9°,  while  the  aver- 
age temperatures  for  February  and  December  were  but 
slightly  less.  In  the  same  year  and  place  other  mini- 
mum temperatures  occurred  as  follows :  February, 
—84.3°  ;  March,  —77.4°  ;  December,  —78.2°  ;  in  the  lat- 
ter month  the  highest  temperature  recorded  was  — 33°. 
This  station  is  situated  in  the  valley  of  the  lana,  at  an 
elevation  of  about  330  feet  above  the  sea.  From  the  lati- 
tude of  the  station  the  sun  is  absent  during  December, 
while  its  elevation  above  the  horizon  for  the  rest  of  the 
winter  is  so  slight  that  the  effect  of  the  direct  rays  of 
the  sun  are  unable  to  counteract  the  intense  cold  caused 
by  radiation.  As  might  be  expected,  the  percentage 
of  cloudiness  is  small  during  the  winter  months,  averag- 
ing about  38  per  centum,  and  being  least  in  January, 
the  month  of  greatest  cold.  Usually  the  weather  is 
perfectly  calm.  In  January,  1886,  87  calms  were  re- 
ported in  91  observations,  and  in  December  63  calms 
out  of  85  observations. 

During  January,  1886,  which  was  an  unusually  cold 
month  for  Siberia,  very  low  temperatures  were  ob- 
served elsewhere,  as  follows  :  Banscht  Schikowo,  58° 
N.,  109°  E.,  —80.5°  ;  Marchinskoe,  62°  N.,  130°  E., 
-78.7°  ;  Olekminsk,  60°  22'  1ST.,  59°  E.,  —69°. 

It  is  a  common  belief  that  the  cold  of  the  Arctic  archi- 
pelago, in  the  neighborhood  of  the  North  Pole,  is  more 
intense  during  the  winter  than  in  the  interior  of  great 
continents,  but  such  an  opinion  is  not  substantiated  by 
the  records  of  lowest  temperatures  observed  by  various 
polar  expeditions,  which  are  as  follows  ;  Mercy  Bay, 


132  AMEKICAN  WEATHEK. 

74°  1ST.,  118°  W.,  January,  1853,  —64.9° ;  Van  Rensselaer 
Harbor,  78.5°  N.,  71°  W.,  February,  1854,  —66.4°  ;  Fort 
Conger,  81.7°  N.,  65°  W.,  March,  1876,  —70.8°,  Feb- 
ruary, 1882,  -62.1°  ;  Floeberg  Beach,  83.5°  1ST.,  61°  W., 
March,  1876,  —73.8°. 

The  character  of  any  climate  is  perhaps  characteris- 
tically shown  in  no  more  forcible  manner  than  by  its 
temperature  variability.  This  is  obtained  by  noting 
the  changes  which  take  place  in  the  mean  daily  tem- 
perature from  day  to  day,  regardless  of  the  fact  whether 
the  temperature  rises  or  falls.  The  sum  of  these 
changes  for  any  month  divided  by  the  number  of  days 
in  the  month  gives  the  variability  of  temperature  for 
that  month,  and  from  a  number  of  years  the  average 
variability  is  satisfactorily  obtained.  As  a  rule,  the 
variability  is  greatest  in  January  over  the  United 
States,  and  least  in  either  July  or  August.  January 
has  been  selected  as  showing  the  most  unfavorable 
phases  of  temperature  variability,  although  the  vari- 
ability is  slightly  larger  for  February  in  the  greater 
part  of  Michigan,  Western  New  York,  Pennsylvania, 
New  Jersey,  Maryland,  Delaware,  and  Eastern  Vir- 
ginia. It  is  evident  that  the  only  portions  of  the  United 
States  where  the  changes  from  day  to  day  are  not  of  a 
very  decided  character  is  the  Pacific  coast  region,  Ari- 
zona, and  Southern  Florida.  The  most  equable  stations 
are  those  situated  on  the  immediate  Pacific  coast, 
where  the  change  from  day  to  day  barely  equals  two 
degrees.  In  striking  contrast  to  these  equable  tem- 
perature conditions  may  be  noted  the  entire  Missouri 
and  extreme  Upper  Mississippi  Valleys,  where  during 
January  the  average  change  to  warmer  or  colder  from 
one  day  to  another  ranges  from  8°  to  10°.  The  severest 
changes  are  experienced  in  Western  Minnesota,  Dakota, 
Montana,  and  Western  Idaho,  over  the  greater  part  of 


AMERICAN   WEATHER.  133 

j 

which  the  differences  from  day  to  day  nearly  amount 
to  ten  degrees.  The  largest  winter  difference  in  the 
entire  country  occurs  at  Eastport,  a  station  noted 
for  its  equable  temperature  conditions  during  August 
and  September,  but  which  averages  nearly  12°  for  Jan- 
uary and  10°  for  February. 

During  July  and  August  the  variability  is  small 
throughout  the  entire  United  States,  and  along  the 
Pacific,  Gulf,  and  South  Atlantic  coasts  amounts  on 
the  average  to  only  a  degree  and  a  half  ;  the  smallest 
being  1.0°  at  San  Diego,  and  the  largest  2.0°  at  Jack- 
sonville. The  largest  summer  ranges  are  found  in 
Lake  Superior  region,  Dakota,  and  Montana,  gener- 
ally varying  between  four  and  six  degrees. 


CHAPTER  XI. 

DISTRIBUTION   OF   KAIN   AND    SNOW. 

ALTHOUGH  rainfall  is  comparatively  a  local  pheno- 
menon, yet  in  order  to  give  an  adequate  idea  of  its 
general  distribution,  it  is  necessary  to  assume  that  from 
observations  made  at  scattered  stations  we  can  obtain 
fairly  accurate  opinions  as  to  the  precipitation  occur- 
ring over  extensive  intervening  areas. 

Chart  No.  XI.  shows  the  mean  annual  rainfall  for 
the  land  surface  of  the  Northern  Hemisphere.  The 
heaviest  rainfalls  in  the  world  are  found  on  the  west- 
ern or  southern  coasts  of  the  Eastern  and  Western  Hemi- 
spheres contiguous  to  the  seas.  The  prevailing  winds 
bring  the  aqueous  vapor  that  is  so  copiously  de- 
posited along  the  immediate  coasts  of  these  regions. 
In  low  latitudes  the  prevailing  northeast  trades  also 
bring  heavy  rainfalls,  as  appears  along  the  northern 
coast  of  South  America  and  Central  America.  The 
least  rainfall  (five  inches  or  less)  occurs,  where  it  might 
be  reasonably  expected,  in  the  North  Polar  regions, 
where  the  very  low  mean  temperature  permits  the  air 
to  contain  but  a  comparatively  small  amount  of  aque- 
ous vapor.  Detached  localities  to  the  leeward  of  moun- 
tain ranges  in  the  interior  of  great  continents,  such  as 
Asia  and  America,  are  also  as  scantily  favored  with 
rainfall  as  the  Arctic  regions. 

From  carefully  collated  data  John  Murray,  Esq. ,  has 
estimated  that  over  twenty-two  per  centum  of  the 
land  areas  of  the  earth  has  less  than  ten  inches  of 


AMERICAN   WEATHER.  135 

rain  annually  ;  over  thirty-one  per  centum  has  from 
ten  to  twenty-five  inches  fall ;  sixteen  per  centum, 
from  fifty  to  seventy-five  inches,  and  six  per  centum 
has  over  seventy-five  inches.  The  highest  mean  rain- 
fall occurs  in  Sumatra,  about  130  inches  ;  the  least  in 
Greenland,  15.5  inches,  closely  followed  by  Australia, 
15.7.  In  North  America  only  sixteen  per  centum  of  the 
area  has  under  ten,  and  less  than  two  per  centum  over 
seventy-five  inches  of  rain. 

The  annual  average  rainfall,  including  melted  snow, 
over  the  United  States  varies  in  different  sections  of 
the  country  from  less  than  four  inches  to  more  than  one 
hundred  inches  ;  the  quantity  depending  largely  on 
the  elevation,  distance  from  the  ocean,  and  the  direc- 
tion either  of  the  prevailing  wind  of  the  locality,  or  on 
accidental  winds  caused  by  the  passage  of  storm  cen- 
tres across  the  country. 

In  the  United  States  the  last-mentioned  condition 
is  the  most  conducive  to  rainfall,  for  while  precipita- 
tion is  occasionally  fed  by  local  evaporation,  yet  its 
preponderating  source  is  found  in  the  vapor-laden 
winds  from  the  ocean  or  inland  seas.  It  thus  results 
that  the  centre  of  aspiration  induces  winds  favorable 
for  rainfall  in  some  quarters  and  unfavorable  in  others. 
Blanford  has  pointed  out  that  Kurrachee,  with  a 
steady  monsoon  wind  of  400  miles  daily,  is  not  neces- 
sarily favored  with  precipitation  ;  but  that  in  India 
deflections  of  the  wind  from  its  normal  direction  by 
local  irregularities  of  pressure  increase  the  probability 
of  rain  in  proportion  to  the  amount  of  such  deflection. 

There  is  probably  no  part  of  the  face  of  the  globe 
where  such  an  enormous  area  of  country  is  favored 
with  moderate  rains— from  thirty  to  sixty  inches  a 
year — as  that  portion  of  the  United  States  to  the  east- 
ward of  the  97th  meridian.  From  Minnesota,  Iowa, 


136  AMERICAN   WEATHER. 

and  Missouri,  eastward  to  the  Atlantic  coast,  the  an- 
nual rainfall  varies  from  thirty  to  forty-five  inches. 
Southward  of  the  37th  parallel  the  quantity  of  rain 
yearly  is  somewhat  greater,  ranging  generally  between 
forty-five  and  sixty  inches. 

It  is  a  general  and  tolerably  accurate  rule  that  the 
rainfall  in  the  United  States  decreases  with  increasing 
distance  from  the  ocean,  and  so  incidentally  with  the 
elevation  ;  but  the  variations  are  markedly  different  on 
the  Pacific  coast  from  those  to  the  eastward  of  the 
Rocky  Mountains.  Along  the  Pacific  coast  the  rain- 
fall is  greatest  at  the  extreme  northwestern  point,  and 
decreases  quite  regularly  with  the  latitude,  being  least 
at  the  extreme  southwestern  part.  Contrary  to  this 
rule,  the  rainfall  of  the  Atlantic  coast,  with  local  excep- 
tions, decreases  from  south  to  north. 

An  annual  rainfall  exceeding  forty -four  inches  occurs 
along  the  Atlantic  coast  and  Gulf  coast,  in  the  valleys 
of  the  Lower  Mississippi,  Lower  Ohio,  Cumberland, 
Tennessee,  and  Lower  Arkansas  rivers,  and  along  the 
Pacific  coast  to  the  northward  of  the  40th  parallel. 
Except  in  a  few  favored  spots,  such  as  the  Yellowstone 
Park,  the  rainfall  is  less  than  twenty  inches  over  the 
country  situated  between  the  100th  and  the  121st  me- 
ridians. In  Southern  Nevada,  Southeastern  California, 
Western  Arizona,  and  Southwestern  Utah,  to  the  lee- 
ward of  the  mountain  ranges,  less  than  eight  inches 
fall  annually,  and  in  certain  localities  even  less  than 
three  inches. 

The  astonishing  increase  of  rainfall  along  the  Pacific 
coast—from  twelve  inches  at  San  Diego  to  twenty-four 
at  San  Francisco,  eighty-three  at  the  mouth  of  the 
Columbia  Biver,  and  one  hundred  and  five  inches  at 
Neah  Bay,  Wash.  Terr.— is  a  striking  climatic  charac- 
teristic of  that  region.  Indeed,  Cape  Flattery,  the 


AMERICAN  WEATHEK.  137 

northwestern  point  of  the  United  States,  may  be  called 
a  maximum  rain  centre,  since  from  it  the  rainfall  di- 
minishes in  all  directions  to  the  eastward  and  south- 
ward. 

The  heaviest  rainfall  in  that  section  occurs  on  the 
immediate  coast  during  the  winter,  when  monthly 
rainfalls  exceeding  twenty  inches  are  not  very  unusual 
at  exposed  points.  Yearly  falls  of  100  inches  or 
more  are  of  record  at  several  points,  and  the  annual 
rainfall  at  Neah  Bay  is  105.2  inches.  The  following 
are  the  falls  exceeding  100  inches  for  single  years  : 
WasJiington  Territory :  Neah  Bay,  1865-66  (season), 
140.9  inches  ;  Tatoosh  Island,  1886-87,  112.9.  Cali- 
fornia :  Nevada  City,  1867-68,  115.3  ;  Crescent  City, 
1881-82,  113.4  ;  Bowman's  Dam,  1871-72,  102.2.  Ore- 
gon: Astoria,  1875-76,  112.5.  In  the  United  States 
other  heavy  rainfalls  for  a  single  year  are  those  of 
Point  Pleasant,  La.,  1880-81  (ten  months  only),  102.4, 
and  at  Baton  Rouge,  La.,  1846,  116.4  inches. 

Rainfalls  exceeding  100  inches  have  been  recorded 
in  twelve  consecutive  months  at  exposed  stations 
in  the  Atlantic  States,  among  which  may  be  men- 
tioned Mount  Washington,  129.23  inches,  1879-80 ; 
Cape  Lookout,  113.92,  1877-78,  and  Cape  Hatteras, 
102.39,  1877-78. 

Although  the  annual  rainfall  at  certain  places  along 
the  Pacific' coast  seems  very  large,  yet  the  average  at 
some  points  on  the  west  coast  of  Ireland  and  Scotland 
is  more  excessive.  At  Seathwaite,  Borrowdale,  the 
average  annual  fall  amounts  to  154  inches.  India,  how- 
ever, far  exceeds  the  rest  of  the  world  in  the  amount 
of  annual  precipitation.  The  immediate  southwest 
coast  of  India  bordering  the  Arabian  Sea,  nearly  all  of 
British  Burmah  and  Sumatra,  have  average  annual 
rainfalls  exceeding  100  inches. 


138  AMERICAN  WEATHEK. 

The  rainfall  of  Cherrapunji,  Assam,  India,  averages 
493.2  inches  per  year,  the  largest  in  the  world.  This 
enormous  rainfall  is  owing  to  the  station  being  situated 
on  the  side  of  a  mountain,  which  rises  very  precipi- 
tously 4000  feet,  so  that  the  aqueous  vapor  of  the  ascend- 
ing air  of  the  southwest  monsoon  is  condensed  by  the 
cold  of  expansion,  and  the  rain  is  deposited  in  tor- 
rents. At  this  station  in  August,  1841,  264  inches,  or 
twenty-two  feet  of  rain,  fell,  and  in  five  successive 
days  there  was  precipitation  to  the  amount  of  thirty 
inches  in  every  twenty-four  hours.  It  is  stated  that  in 
1860,  699.7  inches,  or  58.3  feet,  fell  at  this  station,  and 
in  1861  occurred  the  enormous  and  almost  incredible 
amount  of  905.1  inches,  or  75.5  feet.  Since  1871  the 
rainfall  has  been  measured  by  a  government  official, 
and  so  may  be  considered  fairly  trustworthy  and  ac- 
curate, and  in  this  period  the  annual  rainfall  at  Cher- 
rapunji has  varied  from  551.9  inches  to  283.0  inches, 
with  a  maximum  monthly  rainfall  of  184.8  in  June, 
1876.  On  June  14th,  1876,  40.6  inches  fell  in  twenty- 
four  hours,  an  average  of  1.7  inches  per  hour. 

Probably  the  smallest  rainfalls  in  the  world  occur  in 
Southeastern  California  and  Western  Arizona,  in  and 
near  the  valley  of  the  Lower  Colorado,  and  in  the 
section  known  as  the  Mohave  Desert.  The  stations 
which  have  annually,  during  the  season  from  July  to 
June,  inclusive,  falls  of  rain  less  than  three  inches, 
are*:  Yuma,  Ariz.,  2.81  inches  ;  Bishop  Creek,  Inyo 
County,  CaL,  2.02  ;  Indio,  San  Diego  County,  Cal., 
1.92 ;  Mammoth  Tank  (same  county),  1.88 ;  Camp 
Mohave,  Ariz.,  1.85  inches.  These  last  two  stations 
doubtless  have  the  smallest  known  rainfall  on  the  face 
of  the  globe.  Statements  have  been  frequently  made 
that  rain  never  falls  in  these  localities,  but  there  is 
no  year  at  any  station  where  a  measurable  rainfall  has 


5  ^  ,  LW-«-» 


AMERICAN   WEATHER.  139 

not  been  recorded,  the  least  observed  being  that  at 
Indio,  0.10  inch,  during  the  seasonal  year  1884-85. 
Similar  stories  to  the  effect  that  no  rain  falls  for  years 
in  parts  of  Spain,  Arabia,  Thibet,  and  Southwestern 
Siberia  may  be  considered  exaggerated  and  unreliable. 
The  smallest  recorded  annual  rainfall  in  Spain  is  six 
inches.  Aden,  Arabia,  from  four  years'  observations, 
has  a  mean  rainfall  of  2.36  inches  ;  Leh,  Ladakh,  ad- 
joining Thibet,  has  a  mean  of  2.62  inches,  from  nine 
years'  observations,  and  Petro  Alexandrowsk,  IS".  41.5°, 
E.  61°,  2.44  inches.  The  author  knows  of  no  other 
stations  in  the  Northern  Hemisphere  where  the  annual 
mean  rainfall,  from  recorded  observations,  is  less  than 
three  inches. 

The  United  States,  in  addition  to  having  over  the 
greater  part  of  its  surface  a  moderate  rainfall,  is  also 
favored  in  the  distribution  of  rain  throughout  the 
year,  which  generally  is  as  equable  in  its  variation  as 
the  annual  amounts.  In  order  to  better  treat,  in  a 
general  manner,  the  distribution  of  rainfall  throughout 
the  entire  year,  the  writer  has  considered  a  wet  month 
as  being  one  in  which  fifty  per  centum  more  rain,  and 
a  dry  month  one  in  which  fifty  per  centum  less  of  the 
annual  rain  falls  than  the  average.  In  like  manner,  a 
very  wet  month  is  one  in  which  double  the  amount  of 
rain  falls,  and  a  very  dry  month  one  in  which  less 
than  one  quarter  of  the  average  rainfall  occurs.  That 
is  to  say,  8.33  per  centum  of  the  annual  rainfall  is  the 
proportional  amount  for  each  month,  so  that  a  month 
with  12.5  per  centum  of  the  average  yearly  rain  is  wet ; 
with  16.7  very  wet ;  with  4.2  dry,  and  with  2.1  per 
centum,  or  less,  very  dry. 

So  treated,  it  appears  that  there  is  no  section  of  the 
country  from  the  Atlantic  Ocean  westward  to  Michi- 
gan, Indiana,  Missouri,  Arkansas,  and  Louisiana, 


140  AMEKICAH  WEATHER. 

whicli  has  on  an  average  either  a  very  dry  or  a  very 
wet  month,  and  only  a  few  localities  even  have  a  wet 
month.  February  is  wet  in  Kentucky  and  Tennessee  ; 
March  in  Alabama  and  Georgia,  and  August  along  the 
immediate  Atlantic  and  East  Gulf  coasts. 

There  is  a  well-marked  tendency  in  Illinois,  Iowa, 
the  entire  Missouri  Valley,  Nebraska,  and  Kansas  to 
have  a  very  wet  May  and  June,  or  June  and  July. 
Along  the  valley  of  the  Upper  Rio  Grande  and  in  Ari- 
zona, July  and  August  are,  relatively  speaking,  very 
wet  months  for  these  localities,  while  the  Pacific  coast 
region  has  a  very  wet  December  and  January  in  the 
northern  part,  and  January,  February,  and  March  in 
the  lower  portion.  Very  dry  months  prevail  over  the 
eastern  slope  of  the  Rocky  Mountains  from  Dakota 
southward  to  Western  Texas  during  December  and 
January.  In  Arizona  June  is  very  dry,  in  Utah,  July, 
and  in  Oregon,  August.  In  California  the  months  of 
June,  July,  August,  and  September  are  likewise  very 
dry. 

In  order  to  illustrate  graphically  for  the  year  the 
peculiarly  varying  distribution  of  rain  in  the  United 
States,  the  monthly  mean  rainfall  for  six  widely  sep- 
arated stations  have  been  charted  in  Fig.  23.  As  far 
as  possible  they  are  representative  stations  as  to  local- 
ity, and  are  otherwise  typical. 

The  rainfall  curves  of  the  United  States,  thus  charted, 
represent  several  characteristic  types.  The  Pacific 
type,  which  obtains  in  the  Pacific  coast  region,  has  a 
very  marked  winter  maximum  and  an  equally  decided 
summer  minimum  ;  it  is  here  represented  by  the  San 
Francisco  curve. 

Along  the  Pacific  coast  of  the  United  States  the 
summer  is  a  thoroughly  dry  season,  as  rain  rarely  falls. 
The  frequency  of  rain  and  the  length  of  the  rainless 


AMERICAN  WEATHEK. 


141 


T)plcal  Annual  Muctuadon  of  RalnfalL 


FIG. 


period  become  the  more  pronounced  from  British.  Co- 
lumbia southward  to  Southern  California,  and  in  the 
southern  portions  of  California  the  dry  season  is  often 


142  AMERICAN   WEATHER. 

unbroken,  even  by  a  single  passing  shower,  from  May 
to  October. 

The  trans-Mississippi  type,  though  less  decided,  as 
shown  by  the  Omaha  curve,  is  exactly  the  reverse  of 
the  Pacific  curve,  as  it  has  its  maximum  in  summer  and 
minimum  in  winter.  Arizona,  contrary  to  the  gener- 
ally received  opinion,  owing  to  its  situation,  does  not 
fall  under  the  same  rain  conditions  as  the  States  bor- 
dering on  the  Pacific.  Though  the  winter  is  marked 
by  occasional  rains,  yet  far  the  heaviest  rainfall  occurs 
in  midsummer.  It  will  be  found  to  have  a  curve  with 
a  double  inflection,  as  shown  by  the  diagram  for  Fort 
Grant,  where  the  characteristics  of  both  the  Pacific  and 
trans-Mississippi  types  appear  combined. 

The  Atlantic  type,  while  agreeing  with  the  trans- 
Mississippi  as  to  its  summer  maximum,  is  characterized 
by  a  spring  minimum,  and  is  here  represented  by  New 
York  City. 

As  a  somewhat  important  modification  of  the  pre- 
vailing types  is  to  be  noted  the  rainfall  of  Tennessee 
and  contiguous  territory,  where,  as  is  shown  by  the 
Nashville  curve,  a  very  marked  winter  maximum  is 
followed  by  a  less  decided  spring  minimum. 

At  Gulf  coast  stations  (see  the  Galveston  curve),  the 
maximum  has  a  tendency  to  delay  until  autumn, — the 
period  of  cyclones, — while  the  spring  minimum  of  the 
Atlantic  coast  is  slightly  anticipated. 

The  variation  of  rainfall  for  the  same  month  in  dif- 
ferent years  is  extraordinary  in  some  instances,  espe- 
cially along  the  coasts  where  the  abnormal  course  of 
a  few  low  area  storms  may  enormously  increase  the 
monthly  rainfall,  or  the  absence  of  the  storms  leave 
the  region  substantially  rainless. 

The  effect  of  the  mean  latitude  of  paths  of  low  areas 
upon  the  rainfall  of  a  month  is  shown  by  Hellmann, 


AMERICAN    WEATHER.  143 

where  he  points  out  that  through  such  course  the  rain- 
fall of  the  Spanish  Peninsula  was  ten  times  as  great  in 
January,  1881,  as  during  January,  1882. 

A  similar  contrast  is  offered  between  September, 
1877,  with  three  cyclonic  storm  centres  in  the  south 
Atlantic  States  and  an  average  rainfall  of  9.47  inches 
for  the  district,  as  contrasted  with  September,  1886, 
when  no  storm  centre  passed  over  the  region,  and  the 
average  rainfall  (1.84  inches)  was  less  than  one  fifth  of 
that  in  the  former  year. 

Charts  XIII. ,  XI V.,  and  XY.  show,  for  the  United 
States,  the  average  rainfall  of  April,  May,  and  June, 
as  determined  from  observations  of  the  eighteen  years, 
1870  to  1887,  inclusive. 

These  months  have  been  selected  as  covering  the 
period  during  which  vegetables,  small  fruit,  hay,  and 
the  cereal  crops  are  practically  matured,  while  by  the 
end  of  June  cotton  and  large  fruits  have  reached  a 
decisive  point  in  their  development.  Doubtless  the  cer- 
tainty of  a  crop  and  the  large  productivity  of  the 
eastern  lands  depend  largely  on  the  extreme  regu- 
larity, in  frequency  and  abundance,  of  well-distributed 
showers  in  these  three  months. 

The  striking  feature  of  these  three  charts  is  the 
wonderful  uniformity  of  rainfall.  In  April  the  entire 
Northern  States,  from  Minnesota,  Nebraska,  and  Kan- 
sas, eastward  to  the  Atlantic  Ocean,  are  favored  with  a 
generous  supply  of  rain,  varying  between  the  narrow 
limits  of  two  and  four  inches.  To  the  southward  of 
this  locality  the  average  rainfall  generally  lies  between 
four  and  six  inches,  except  in  Mississippi,  where  it 
varies  from  six  to  nine  inches. 

Far  the  greater  portion  of  the  country  has  a  May 
rainfall  between  two  and  four  inches.  Only  over  a  very 
small  area  does  the  precipitation  exceed  six  inches, 


144  AMERICAN    WEATHER. 

while  the  districts  of  scanty  rainfall  are  substantially 
confined  to  California,  Nevada,  Arizona,  and  New 
Mexico. 

Rainfall  during  June,  a  very  important  growing 
month,  is  quite  large  over  the  entire  country  to  the 
eastward  of  the  Missouri  Valley,  southward  to  Eastern 
Texas.  In  general,  the  June  rainfall  is  not  less  than 
four  inches  and  not  over  six,  the  only  exceptions 
being  local  and  of  limited  extent. 

The  first  rainless  month  for  any  part  of  the  United 
States  is  April,  when  no  precipitation  occurs  in  the  ex- 
treme southeastern  part  of  New  Mexico  and  adjacent 
portions  of  Arizona.  During  May  no  rain  falls  in  the 
extreme  southern  portion  of  Arizona  or  on  the  Mohave 
Desert  of  California.  In  June  all  the  southwestern 
part  of  Arizona  and  the  southern  portion  of  California 
are  entirely  without  rain.  In  July  and  August  no  rain 
falls  in  California  except  in  the  extreme  northern  por- 
tions, but  in  September  the  rainless  belt  is  restricted 
to  the  southern  half  of  California,  and  in  October  to 
the  Mohave  Desert  and  the  extreme  southern  limits  of 
Arizona.  In  Northwestern  Nevada  there  is  a  belt  of 
country  of  above  100  miles  wide,  immediately  eastward 
of  the  Sierra  Nevada,  over  which  no  rain  falls  from 
the  last  of  June  to  the  first  days  of  October. 

In  Table  No.  8  is  given  the  greatest  monthly  rainfall 
recorded  in  each  State  and  Territory. 

Rainfalls  exceeding  ten  inches  in  a  month,  or  two 
and  one  half  inches  in  a  day,  may  be  called  excessive. 
Such  rainfalls  are  most  common  in  the  South  Atlantic 
and  Gulf  States,  from  North  Carolina  to  Texas,  and  in 
the  North  Pacific  coast  region.  They  occur  most  fre- 
quently from  North  Carolina  to  Florida  from  June  to 
September,  inclusive,  and  from  Alabama  westward  to 
Southeastern  Texas  from  March  to  June,  inclusive,  al- 


AMERICAN   WEATHER,  145 

though,  in  the  latter  State  they  sometimes  occur  in 
August  and  September,  in  connection  with  the  advance 
of  West  India  cyclones.  In  Tennessee  such  rains  are 
not  infrequent  from  January  to  April,  and  in  the  coun- 
try immediately  northward  to  the  Ohio  River  from 
May  to  July,  inclusive.  In  the  North  Pacific  coast 
region  such  rainfalls  occur  as  might  be  expected  from 
January  to  March.  From  Virginia  northward  to 
Massachusetts  these  heavy  rains  are  very  infrequent, 
except  during  the  months  of  August  and  September. 
In  the  States  and  territories  not  named,  rainfalls  ex- 
ceeding ten  inches  in  a  single  month,  or  two  and  a 
half  inches  in  twenty-four  consecutive  hours,  are 
of  very  rare  occurrence,  as  appears  from  the  rec- 
ords. 

The  following  are  among  the  heaviest  and  most  ex- 
traordinary  monthly  rainfalls  which  have  been  re- 
corded in  the  United  States  :  Upper  Mattole,  Cal.,  Janu- 
ary, 1888,  41.63  inches,  of  which  25.0  fell  in  three  con- 
secutive days ;  Alexandria,  La.,  June,  1886,  36.9 
inches  ;  Fort  Barrancas,  Fla.,  August,  1878,  30.7 ;  Neah 
Bay,  Wash.  Terr.,  December,  1886,  30.7;  Browns- 
ville, Tex.,  September,  1886,  30.6  ;  Fort  Stevens,  Ore., 
January,  1880,  29.8  ;  Fernandina,  Fla.,  June,  1864, 
28.9;  Newark,  N.  J.,  August,  1843,  22.5;  Merritt's 
Island,  Fla.,  September,  1878,  23.8  ;  Wilmington,  1ST.  C., 
July,  1886,  21.1  ;  Jackson,  Miss.,  April,  1874,  23.8  ; 
Asheville,  N.  C.,  August,  1887,  28.6  ;  Newport,  Ark., 
April,  1886,  21.2  ;  Portland,  Ore.,  December,  1882,  20.1 
inches. 

There  is  scarcely  any  locality  in  the  United  States 
where  rain  to  the  amount  of  two  inches  does  not  occa- 
sionally fall  in  a  single  day,  while  a  fall  of  one  inch  is 
not  unusual.  The  most  excessive  daily  rainfalls  are  as 
follows : 


146  AMERICAN  WEATHER. 

Syracuse,  N.  Y.,  June  8th,  1876,  eight  inches ;  Melissa, 
Tex.,  April  22d-23d,  1879,  eight  inches  ;  Helena,  Ark., 
June  7th-9th,  1877,  twelve  inches,  measured  in  forty 
hours,  and  as  much  more  said  to  have  been  lost ;  New 
Haven,  Conn.,  August  8th-9th,  1874,  8.7  inches  ;  Hat- 
teras,  N.  C.,  August  23d,  1880,  9.1  ;  New  Orleans,  La., 
April  7th-8th,  1880,  9.2  ;  Fort  Wallace,  Kan.,  June 
22d-23d,  1874,  9.3 ;  Mayport,  Fla.,  September  21st, 
1885,  9.5;  September  29th,  1882,  13.7;  Savannah,  Ga., 
August  5th-6th,  1872,  9.6 ;  Memphis,  Tenn.,  June 
8th-9th,  1877,  9.7;  Healdsburg,  CaL,  April  20th-21  st, 
1880,  9.7  ;  Fort  Barrancas,  Fla.,  August  29th,  1878, 
9.8 ;  Brownsville,  Tex.,  September  21st-22d,  1886, 
11.9  ;  September  21st-23d,  23.14  in64|  hrs.  ;  Pensacola, 
Fla.,  June  28th-29th,  1887,  10.7 ;  Brackettville,  Tex., 
October  2d,  1881, 11.0  ;  Lambertsville,  N.  J.,  July  16th, 
1865,  12.1 ;  Point  Pleasant,  La.,  April  5th,  1885,  12.3 ; 
Upper  Mattole,  Humboldt  County,  CaL,  January  29th, 
1888,  6.0  ;  30th,  8.5  ;  31st,  10.5  inches. 

The, most  remarkable  rainfall  recorded  in  the  United 
States  during  twenty-four  hours  is  that  which  occurred 
at  Alexandria,  La.,  June  15th-16th,  1886,  when  21.4 
inches  fell.  This  down-pour  was  not  entirely  local, 
since  13.3  inches  fell  during  the  same  time,  a  few  miles 
to  the  southeastward,  at  Cheneyville.  At  Tridelphia, 
W.  Ya.,  on  July  19th,  1888,  at  the  time  of  excessive 
local  floods,  6.9  inches  of  rain  were  said  to  have  fallen 
in  fifty -five  minutes.  In  any  event  the  local  rainfall 
was  enormous,  as  evidenced  by  the  suddenness  and 
severity  of  the  floods. 

Excessive  as  these  heavy  rainfalls  may  appear,  they 
are  exceeded  in  India,  where,  however,  the  same  pecu- 
liarity obtains  as  in  the  United  States  ;  the  heaviest 
daily  falls  not  occurring  in  the  same  localities,  as  do 
the  heaviest  monthly  rains.  Blanford's  reports  show 
that  at  Delhi,  19.5  inches  fell  September  26th,  1875  ;  at 
Rewah,  30.4,  June  6th,  1882  ;  at  Nagina,  32.4,  and  at 


AMERICAN   WEATHER.  147 

Purneali,  Bengal,  on  September  13th,  1879,  the  unprece- 
dented amount  of  thirty-five  inches  was  recorded. 

The  following  extraordinary  showers,  which,  in  lieu 
of  any  better  term,  may  be  called  down-pours,  indicate 
the  portions  of  the  United  States  where  most  excessive 
rainfalls,  of  rates  ranging  from  five  to  eighteen  inches 
per  hour,  may  be  occasionally  expected. 

Washington,  D.  C.,  June  27th,  1881,  2.34  inches  in  37 
minutes  ;  Philadelphia,  Pa.,  July  26th,  1887,  0.62  inch 
in  seven  minutes  ;  St.  Louis,  Mo.,  August  15th,  1848, 
5.05  inches  in  one  hour  ;  Fort  Scott,  Kan.,  October  2d, 
1881,  1.80  inches  in  twenty  minutes  ;  Osage,  la.,  Au- 
gust 26th,  1881,  1.40  inches  in  fifteen  minutes  ;  West 
Leaven  worth,  Kan.,  July  21st,  1887,  1.90  inches  in 
twenty  minutes  ;  Indianapolis,  Ind.,  July  12th,  1876, 
2.40  inches  in  twenty-five  minutes  ;  Alpena,  Mich., 
September  20th,  1884,  1.05  inches  in  eleven  minutes  ; 
Amanda,  la.,  July  31st,  1878,  1.56  inches  in  fifteen 
minutes;  Fort  Randall,  Dak.,  May  28th,  1873,  1.56 
inches  in  fifteen  minutes  ;  Albany,  N.  Y.,  July  10th, 
1876,  1.12  inches  in  ten  minutes  ;  Portsmouth,  O., 
June  22d,  1851,  1.75  inches  in  fifteen  minutes  ;  New 
York^City,  July  27th,  1873,  and  July  17th,  1877,  0.50 
inch  in  five  minutes  ;  June  5th,  1885,  0.30  inch  in 
three  minutes  ;  May  22d,  1881,  1.15  inches  in  ten  min- 
utes ;  November  18th,  1886,  0.25  inch  in  two  minutes  ; 
Huron,  Dak.,  July  26th,  1885,  1.30  inches  in  ten  min- 
utes ;  Biscayne,  Fla.,  March  28th,  1874,  4.10  inches  in 
thirty  minutes  ;  Newtown,  Del.  Co.,  Pa.,  August  5th, 
1843,  5.50  inches  in  forty  minutes,  and  thirteen  inches 
in  three  hours  ;  Collinsville,  111.,  May  23d,  1888,  1.70 
inches  in  twelve  minutes  ;  Sandusky,  O.,  July  llth, 
1879,  2.25  inches  in  fifteen  minutes  ;  Embarrass,  Wis., 
May  28th,  1881,  2.30  inches  in  fifteen  minutes  ;  Wash- 
ington, D.  C.,  July  26th,  1885,  0.96  inch  in  six  min- 
utes ;  Paterson,  N.  J.,  July  13th,  1880,  1.5  inches  in 
eight  minutes  ;  Galveston,  Tex.,  June  4th,  1871,  3.95 
inches  in  fourteen  minutes  ;  Fort  McPherson,  Neb., 
May  27th,  1868,  two  showers,  one  of  1.50  inches  in  five 
minutes,  and  the  other,  2.25  inches  in  forty  minutes  ; 


148  AMERICAN   WEATHER. 

Concord,  Pa.,  sixteen  inches  in  three  hours,  and 
Brandy  wine  Hundred,  Pa.,  August  5th,  1843,  ten 
inches  in  two  hours. 

The  quantity  of  rain  which  falls  during  twenty- four 
hours,  while  not  a  certain  index  of  the  entire  rainfall 
accompanying  severe  storms,  gives,  'however,  a  good 
idea  of  the  maximum  amount.  The  meteorological 
conditions  under  which  enormously  heavy  rainfalls 
occur  are  such  that  their  prolonged  continuance  is 
quite  unlikely  ;  so  that  storms  are  rare  where  fully 
seventy -five  per  centum  of  the  rain  does  not  fall  in  a 
single  day. 

Among  notable  storms  of  rain  may  be  mentioned 
that  in  New  England  from  February  llth  to  13th,  in- 
clusive, 1886.  During  this  storm,  as  estimated  by  Pro- 
fessor Upton,  five  inches  or  more  of  rain  fell  over 
nearly  5000  square  miles,  and  exceeding  seven  inches, 
occurred  over  1500  square  miles.  During  this  storm 
the  following  amounts  of  rain  fell :  Connecticut :  Hart- 
ford, 8.43  ;  Colebrook,  8.44  ;  New  London,  8.93  ;  Mid- 
dleton,  9.37 ;  Canton,  12.35.  Rhode  Island :  Provi- 
dence, 8.13  inches. 

CLOUD-BURSTS. 

Apart  from  even  exceedingly  heavy  showers  or 
down-pours  may  be  classed  the  enormous  masses  of 
water  which  now  and  then  fall,  and  which  are  popu- 
larly known  in  America  as  cloud-bursts  or  water- 
spouts. In  such  cases  the  amount  of  water  that  falls 
in  an  hour  or  two  must  equal  rainfalls  which  are  other- 
wise deemed  excessive  for  a  day  or  even  for  a  month  in 
the  region.  These  down-pours  of  torrential  rain  are 
fortunately  local,  and  yet  more  fortunately  prevail  in 
the  less  densely  populated  portions  of  the  country. 

Since  the  condensation  of  the  entire  moisture  from 


AMERICAN  WEATHER.  149 

the  atmosphere,  even  when  entirely  saturated  at  60°, 
would  produce  less  than  two  inches  of  rain,  it  follows 
that  an  enormous  amount  of  moist  air  must  be  drawn 
from  adjacent  regions,  in  order  to  render  the  condi- 
tions possible  for  such  excessive  precipitation. 

August  17th,  1876,  at  Fort  Sully,  Dak.,  the  heaviest 
rainfall  ever  known  occurred  ;  and  on  the  opposite  side 
of  the  river  (Missouri),  the  water  draining  from  a  canon 
was  reported  to  have  moved  out  in  a  solid  bank  three  feet 
deep  and  200  feet  wide  ;  August  26th,  1876,  near  Hay's 
City,  Kan.,  a  water-spout  burst  over  Kill  Creek,  caus- 
ing destructive  floods  ;  August  31st,  1876,  on  Chalk 
Creek,  Utah,  five  miles  from  Coalville,  a  cloud-burst  was 
reported,  and  a  solid  bank  of  water,  between  three  and 
four  feet  high,  came  down  the  stream,  destroying  dams, 
etc.  September  12th,  1877,  at  Colorado  Desert,  Cal., 
during  a  heavy  thunderstorm  between  Pilot  Knob  and 
Cactus,  a  water- spout  burst,  destroying  400  feet  of 
railroad-track.  November  16th,  1877,  at  Ked  Bluff, 
Cal.,  after  a  severe  thunderstorm,  attended  by  hail,  a 
water-spout  was  observed.  The  stream  of  water  was 
distinctly  visible,  and  continued  for  about  fifteen  min- 
utes, when  it  gradually  disappeared.  This  occurred 
over  the  open  country,  and  caused  a  stream  of  water 
ten  to  fifteen  feet  in  a  ravine  where  water  is  unknown 
except  during  heavy  rains. 

June  12th,  1879,  on  Beaver  Creek,  ninety  miles  south 
of  Dead  wood,  Dak.,  there  was  a  cloud-burst,  which, 
without  a  gradual  rise  of  water,  in  a  few  minutes  cov- 
ered the  country  and  drowned  eleven  persons. 

At  Seven  Star  Springs,  Mo.,  a  cloud-burst  occurring 
in  hills  above  town  on  June  llth,  1881,  carried  away 
houses  and  drowned  five  persons. 

On  June  22d,  1884,  a  cloud-burst  occurred  near  Jeffer- 
son, Mont.,  causing  a  body  of  water  eight  feet  deep 


150  AMERICAN   WEATHER. 

to  rush  down  on  the  town.  Three  persons  were  drowned 
and  one  quarter  of  a  mile  of  railroad  track  was  washed 
away. 

A  cloud-burst  on  June  10th,  1884,  in  Humboldt 
Mountains,  flooded  valleys  near  Rye  Patch,  Humboldt 
Co. ,  Nev. ,  and  badly  damaged  the  Central  Pacific  track 
for  thirty  miles. 

On  June  8th,  1885,  a  cloud-burst  broke  above  Pason 
de  Cuarenta,  Mexico,  practically  destroying  the  whole 
town  and  drowning  more  than  170  persons  out  of  its 
800  inhabitants. 

It  is  probable  that  cloud-bursts  must  have  occurred 
near  Pittsburg,  Pa.,  the  night  of  July  25th-26th,  1874, 
when  134  lives  were  lost,  and  property  valued  at 
$500,000  was  destroyed. 

July  26th,  1885,  near  Pike's  Peak,  a  cloud-burst  with 
hail-storm,  flooding  a  small  portion  of  Colorado  Springs 
and  drowning  two  persons. 

Near  Wickenburg,  Ariz.,  a  cloud-burst,  causing  the 
Hassayampa  River  from  being  perfectly  dry  at  sun- 
set, August  6th,  1881,  to  be  a  stream  a  mile  wide  at 
11  P.M.,  and  from  two  to  fifteen  feet  deep  ;  in  thirteen 
hours  the  river  was  again  dry. 

On  August  8th,  1881,  a  cloud-burst  occurred  at  Cen- 
tral City,  Col.,  causing  suddenly  a  stream  of  water 
from  four  to  six  feet  in  two  streets. 

The  frequency  and  average  daily  amount  of  rain  are 
quite  important  climatic  characteristics,  since  in  some 
localities  the  rain  falls  infrequently  and  in  heavy  show- 
ers, while  at  other  places  the  rain  falls  often  and  in 
moderate  amounts.  For  instance,  the  average  amount 
of  precipitation  on  each  rainy  day  is  0.25  inch  of  water 
at  Milwaukee,  0.21  inch  at  Eochester,  N.  Y.,  0.19  inch 
at  Pensacola,  Fla.,  and  only  0.12  inch  at  Poplar  River, 
Mont, 


AMEKICAH  WEATHER. 


151 


Probability  of  Rainy  Days, 


FIG.  24. 


The  distribution  of  rainy  days  throughout  the  year 
is  graphically  shown  in  Fig.  24.  The  calculated  per- 
centages of  each  month,  thus  charted  for  selected  sta- 
tions, make  apparent  at  a  glance  the  comparatively 


152  AMERICAN   WEATHER. 

dry  and  wet  periods   of  the  various   districts  of  the 
United  States. 

From  the  Missouri  Valley  eastward  the  number  of 
rainy  days  during  the  year  varies  generally  from  100 
to  140,  exceeding  the  latter  number  only  in  the  lake 
region  ;  especially  along  the  southern  shores  of  Lakes 
Erie  and  Ontario,  where  the  number  of  days  is  as  large 
as  171  at  Rochester  and  177  at  Erie.  The  largest 
number  of  days  occurs  on  the  southeast  side  of  the 
lakes,  showing  the  influence  of  the  prevailing  westerly 
winds  in  bringing  rain.  North  Yolney,  N.  Y.,  with 
a  yearly  average  of  195,  has  probably  the  largest  num- 
ber of  rainy  days  of  any  place  in  the  eastern  part  of 
the  United  States.  There  are  but  134  rainy  days 
at  Milwaukee,  against  152  at  Grand  Haven  ;  136  at 
Toledo,  against  169  at  Buffalo.  The  number  of  rainy 
days  increases  steadily  from  the  Missouri  and  Missis- 
sippi valleys  and  the  Gulf  and  Atlantic  coasts  toward 
Lake  Erie.  Over  the  Rocky  Mountains  and  the  plateau 
regions  the  number  of  such  days  ranges  generally  from 
seventy  to  ninety.  On  the  Pacific  coast  it  rapidly  in- 
creases northward  from  forty-two  at  San  Diego  to 
sixty-six  at  San  Francisco,  186  at  Tatoosh  Island,  224 
at  Sitka,  and  the  astonishing  number  of  250  at  Una- 
laska.  The  lower  drainage  basin  of  the  Colorado 
Grande,  the  southeastern  portions  of  California,  and 
the  southern  part  of  Nevada  show  a  remarkably  small 
number  of  rainy  days,  there  being  but  twenty -two  at 
Keeler,  Cal.,  and  the  minimum  number  of  thirteen  at 
Yuma,  Ariz. 

The  average  number  of  rainy  days  is,  for  each  month, 
at  selected  places,  shown  in  Fig.  No.  24,  from  which 
it  appears  that  at  San  Francisco  the  probability 
of  rain  sinks  steadily  from  a  maximum  of  .40  in 
February  to  less  than  .01  in  July  and  August.  The 


AMERICAN   WEATHEK.  153 

curve  at  Tatoosh  Island  is  similar  in  character,  since 
its  maximum  occurs  in  winter — .80  in  December,  and 
the  minimum  of  .19  in  August.  The  chances  of  rainy 
weather  in  the  lake  region  are  represented  by  the 
curve  for  Erie,  the  summer  minimum  and  winter  max- 
imum being  clearly  outlined.  The  Jacksonville  curve 
is  peculiar  in  that  the  probability  of  a  rainy  day  in- 
creases during  the  summer,  being  about  .45  from  June 
to  September,  inclusive,  and  sinking  to  a  minimum  of 
.43  in  December  and  April,  with  an  intervening  sec- 
ondary maximum  in  February.  The  chances  of  rainy 
weather  in  the  country  from  the  Mississippi  Valley 
eastward  varies  but  little  during  the  year,  except  in 
the  lake  region,  as  shown  by  the  Erie  curve.  Boston 
and  Chicago  are  so  closely  in  accord  that  their  means 
have  been  consolidated,  and  they  are  represented  by 
one  curve,  which  varies  less  than  two  per  centum  for 
any  month  in  the  year  from  either  mean.  The  prob- 
ability of  rain  on  any  day  in  March  is  .41  at  these 
places,  while  that  for  September  is  but  .32,  showing 
how  fine  and  free  from  rain  is  the  autumn  weather. 
The  Yuma  curve  is  interesting,  with  its  double  maxi- 
mum, in  February  and  August,  of  .08  only,  and  its  dou- 
ble minimum  of  .02  in  October  and  .01  in  May  and  June. 

The  variability  of  rainfall  is  an  important  question 
for  all  agricultural  interests,  since  an  annual  rainfall 
of  twenty  inches  may  mean  a  fall  of  thirty  inches  for 
several  years,  followed  by  years  of  fifteen  inches  or  less. 

Blanf ord  points  out  that  in  India  a  province  is  liable 
to  severe  famine,  and  consequent  drought,  if  with  an 
annual  rainfall  under  fifty  inches  its  mean  annual  devi- 
ation exceeds  twelve  per  centum,  in  excess  or  defect. 

Blanford's  method  of  determining  the  mean  annual 
deviation,  while  not  free  from  objection,  is  used  by 
the  author  for  the  sake  of  uniformity.  Instead  of 


154: 


AMEKICAN  WEATHER. 


striking  a  mean  from  the  sum  of  all  departures,  whether 
plus  or  minus,  he  calculates  a  mean  from  the  excesses 
and  another  from  the  minus  departures,  and  takes  half 
these  averages  as  the  mean  annual  deviation. 

The  following  table  shows  the  mean  ^annual  devia- 
tion of  rainfall  at  certain  selected  stations  which  are 
fairly  representative  of  different  sections  of  the  United 
States  : 


Tears  of 
Observation. 

Stations. 

Mean  Annual 
Rainfall. 

Deviation. 

Per  Cent,  of 
Mean  Annual 
Deviation. 

59 

Troy.  N.  Y  

36  31 

496 

14 

17 
17 
16 
17 
16 
17 

New  York  City.  . 
Washington  City. 
Jacksonville,  Fla. 
New  Orleans,  La. 
Nashville,  Tenn.. 
Detroit  Mich  

43.86 
43.84 
57.15 
63.82 
52.10 
3357 

4.5 
6.76 
5.32 
5.34 
6.06 
6  00 

9 
15 
9 
8 
12 
18 

17 

St  Louis  Mo 

38  56 

5  60 

15 

16 

St.  Paul,  Minn  

28.63 

4.08 

14 

17 

Omaha  Neb  

34  68 

7.10 

20 

16 

Denver  Col 

14  90 

2  SQ 

16 

16 

Portland  Ore      .... 

51  65 

6  72 

13 

10 

16 

Sacramento,  Cal  
San  Diego  Cal 

21.73 

10  81 

5.38 
408 

25 
37 

11 

Yuma,  Ariz..  .  . 

2  92 

1  37 

47 

It  is  noticeable  that  the  percentage  of  deviation  is 
exceedingly  small  along  the  Atlantic  sea-coast  and  on 
the  shores  of  the  Gulf  of  Mexico.  This  small  variabil- 
ity is  a  reliable  indication  that  such  sections  are  free 
from  prolonged  and  disastrous  droughts.  Even  as  far 
west  as  the  Mississippi  Yalley  the  deviation  is  small, 
rarely  exceeding  fifteen  per  centum,  and  at  Denver  is 
but  sixteen  per  centum,  showing  a  constancy  of  rain 
conditions  not  often  credited  to  that  section  of  the 
country.  In  the  Pacific  coast  region  the  variability  of 
the  rainfall  is  greater  than  obtains  in  any  other  part 
of  the  country.  In  that  section  the  rainfall  is  sea- 
sonal, the  greater  part  of  it  falling  in  winter,  so  that 


AMERICAN   WEATHER.  155 

the  deviation  is  determined  from  the  seasonal  rainfall 
between  July  1st  and  June  30th.  The  fall  in  the  wettest 
year  at  Sacramento,  where  the  deviation  is  twenty-five 
per  centum,  was  4.5  times  greater  than  that  in  the  least 
year,  and  at  San  Francisco  six  times.  As  a  rule,  the 
greatest  deviation  is  found  with  a  small  annual  rain- 
fall, and  Yuma,  Ariz.,  with  2.92  inches  a  year,  has  a 
deviation  of  forty-seven  per  centum. 

Blanford  has  carefully  determined  the  hourly  fluc- 
tuations of  the  amount  of  rainfall  at  Calcutta,  from 
observations  of  seven  years,  1878-84,  inclusive.  It  has 
likewise  been  fixed  by  Draper  for  New  York  City,  from 
observations  during  the  seven  years  1870-76,  inclu- 
sive. The  results  of  Draper's  observations  appear  in 
Fig.  25,  where  the  departures  are  charted.  Both  in 
Calcutta  and  New  York  the  amount  of  rain  is  greater 
from  noon  to  midnight  than  from  midnight  to  noon. 
The  fluctuations  throughout  the  day  are  closely  in 
accord  at  both  places.  The  primary  and  secondary 
maxima  fall  at  Calcutta  from  5  to  8  P.M.  and  2  to 
5  A.M.,  and  at  New  York  from  4  to  7  P.M.  and  2  to 
5  A.M.  The  minima  at  Calcutta  occur,  primary  from  10 
to  12  P.M.,  secondary,  8  to  10  A.M.  ;  at  New  York,  sec- 
ondary, 10  to  12  P.M.,  primary,  5  to  7  A.M. 

The  tendency  is  well  marked  at  both  stations  for 
precipitation  to  occur  in  larger  quantities  after  the  air 
has  passed  its  highest  temperature  and  is  cooling  most 
rapidly,  near  and  after  sunset. 

The  question  of  the  influence  of  vegetation  and  for- 
ests upon  rainfall  is  a  vexed  one,  and  from  its  charac- 
ter is  not  susceptible  of  positive  proof  or  disproof. 
The  influence  of  forests  on  rainfall  or  temperature 
must  depend  on  the  extent,  density,  and  character  of 
the  woodland  growth.  The  evaporating  and  absorptive 
powers  of  foliage  necessarily  vary  with  the  species, 


156 


AMERICAK   WEATHER. 


and  are  also  dependent  for  nearly  half  the  year  on 
the  amount  of  persistent  leaves.  There  is  no  ques- 
tion but  that  the  presence  of  vegetation  subserves 


lM^^ 

1870-1S7B 


.030 


+.Q1Q 


,020 


.030 


2  3£  5  6T8910  11121  2 


78  91OD 


FIG.  25. 


the  conservation  of  rainfall  and  aids  in  its  regu- 
lar and  systematic  distribution.  As  has  been  inti- 
mated in  treating  upon  dew,  the  amount  of  precipi- 
tation is  increased  in  some  sections  to  no  inconsiderable 


AMEKICAK   WEATHER.  157 

extent  by  deposition  in  the  form  of  dew  upon  the 
growing  vegetation.  Since  the  precipitation  of  a  coun- 
try is  increased  by  the  deposition  of  dew,  and  as  the 
vegetation  absorbs  the  moisture,  instead  of  allowing  it 
to  pour  into  adjacent  river-beds  in  rapid  torrents,  it 
necessarily  follows  that  local  evaporation  is  by  this 
manner  increased.  While  the  amount  of  increase  may 
be  small  in  some  cases,  yet  it  must  be  considerable  in 
others,  and,  as  Blanford  has  pointed  out,  in  India  the 
rainfall  in  some  sections  is  fed  to  no  inconsiderable  ex- 
tent by  local  evaporation. 

As  regards  the  influence  of  forests,  Woiekoff  has 
pointed  out  that  they  assist  in  storing  the  water  by 
protecting  the  soil,  and  thus  maintain  constant  evapo- 
ration, and  that  the  presence  of  the  forests  materially 
modifies  the  wind  movement,  thus  preventing  the 
transference  of  evaporated  vapor  to  other  points,  while 
also  tending  to  induce  calms,  which  are  so  favorable  to 
ascending  currents  and  local  precipitation. 

The  importance  of  this  last  condition  is  set  forth  by 
Blanford,  who  instances  the  heavy  spring  rainfalls  of 
Assam,  which  result  from  direct  diurnal  convection 
of  the  humid  atmosphere  and  its  consequent  dynamic 
cooling  and  precipitation. 

Fortunately  for  elucidation  of  this  question,  the  fire- 
devastated  forests  of  the  central  provinces  of  India  have 
within  the  past  twelve  years  been  replaced  by  exten- 
sive growth  of  young  forests,  covering  54,000  square 
miles.  Twenty-two  rainfall  stations  are  maintained 
over  this  area,  with  records  covering  the  past  eighteen 
years.  It  appears  from  these  observations  that  the 
rainfall  for  this  province  has  progressively  increased 
with  the  growth  of  the  forest,  and  apparently  is  twenty 
per  cent  largertj.ajx^e^average  for  ten  previous  years. 
lB,  forest  in  the  Punjab,  covering 


158  AMERICAN   WEATHER. 

17,000  acres,  indicate,  by  a  register  within  the  forest, 
an  excess  of  six  per  cent  over  the  probable  rainfall  as 
computed  from  the  rainfall  registers  of  two  stations, 
respectively,  four  and  thirteen  miles  distant  from  the 
forest.  While  the  evidence,  as  Blanford  says,  "  is  not 
rigorously  conclusive, "  yet  the  author  believes  with  him 
that  the  long-suspected  influence  of  forests  on  rainfall 
is  no  longer  a  question  of  equally  balanced  proba- 
bilities. 

Unfortunately,  there  are  no  such  statistics  available 
in  the  United  States  as  in  India,  nor  under  as  favor- 
able conditions,  but  the  writer  believes  that  the  exten- 
sive cultivation  of  the  soil  and  the  development  of  the 
Western  territories  has  increased  in  some  degree  the 
rainfall  west  of  the  Mississippi  River,  through  the 
medium  of  largely-increased  vegetation  and  through 
the  enormous  increase  of  scrub  growth,  fruit  and  forest 
trees,  which  has  resulted  partly  from  the  discontinu- 
ance of  extensive  prairie  fires,  and  in  greater  part  by 
the  intelligent  planting  done  by  enterprising  pioneers. 

DISTRIBUTION   OF   SNOW. 

The  limitations  of  temperature  are  such  that  snow  is 
practically  impossible  over  two  thirds  the  land  surface 
of  the  earth.  It  is  evident  that  snow  may  occasionally 
fall  during  very  low  temperatures  in  very  low  latitudes, 
but  such  phenomenon  must  be  very  rare  in  places  where 
the  mean  temperature  of  the  day  does  not  sink  for 
some  portion  of  the  year  below  32°.  The  northern 
parallel  of  latitude  at  which  snow  never  falls  is  not 
the  same  for  all  localities,  but  depends  on  elevation, 
nearness  to  the  sea,  and  other  causes. 

The  lowest  latitude  where  snow  has  been  known  to 
fall  on  land  of  slight  elevation  is  in  the  neighborhood 


AMERICAN   WEATHEK.  159 

of  Canton,  China,  near  the  23d  parallel  of  N".  latitude, 
within  the  tropics. 

The  United  States  is  so  situated,  however,  that  snow 
occurs  more  or  less  frequently  over  almost  the  entire 
country.  The  southeastern  part  of  Florida  is  the  only 
portion  of  the  country  where  this  phenomenon  has  not 
been  witnessed.  Even  as  far  south  as  Punta  Rassa, 
Fla. ,  within  less  than  a  hundred  miles  of  Key  West,  snow 
fell  for  about  five  minutes  on  December  1st,  1876  ;  and 
at  San  Diego,  Cal.,  during  the  great  snow-storm  of 
January  15th-17th,  1882,  snow  flakes  were  for  a  short 
time  seen  descending.  Although  snow  is  thus  pos- 
sible over  almost  the  entire  country,  yet  it  may  be  said 
to  be  practically  unknown  along  the  immediate  Cali- 
fornia coast  from  San  Francisco  southward,  and  along 
the  Atlantic  coast  from  central  Georgia  southward.  It 
occasionally  occurs  in  considerable  quantities  on  the 
Atlantic  coast,  even  as  far  south  as  Savannah,  and 
along  the  coast  of  the  Gulf  of  Mexico,  from  Pensacola, 
Fla.,  to  Brownsville,  Tex.  (25°  53'  K).  But  in  these 
sections  it  is  not  a  phenomenon  which  recurs  regularly 
year  by  year.  It  is  a  general  rule  that  snow  does  not 
fall  in  sufficient  quantities  to  lie  upon  the  ground  to 
the  southward  of  the  33d  parallel,  except  in  mountain- 
ous and  elevated  places,  nor  within  about  fifty  miles 
of  the  sea,  as  far  northward  as  the  35th  parallel  on  the 
east  and  the  38th  parallel  on  the  west  coast. 

The  annual  amount  of  snow  is  not  constant  for  any 
locality,  as  it  is  dependent  not  only  on  the  length  and 
severity  of  the  weather,  but  also  upon  the  frequency 
and  violence  of  atmospheric  disturbances  which  cause 
precipitation.  The  newly  fallen  snow  has  a  very  small 
specific  gravity,  so  that  ten  or  twelve  inches  of  it  when 
melted  are  equal  to  only  one  inch  of  water. 

The  quantity  of  snow  which  falls  annually  over  the 


160  AMERICAN   WEATHEK. 

northern  half  of  the  United  States  varies  greatly  from 
year  to  year,  and,  as  a  rule,  decreases  from  Maine 
westward  to  the  Rocky  Mountain  region.  Assuming 
that  the  precipitation  which  occurs  from  December 
to  February,  inclusive,  in  the  northern  part  of  the 
United  States  is  in  the  form  of  snow,  it  appears  that 
the  average  annual  snowfall  may  be  placed  at  seven  to 
eight  feet  in  Maine,  six  to  seven  feet  in  New  York,* 
four  to  five  feet  in  Michigan,  three  to  four  feet  in  Iowa, 
two  to  three  feet  in  Minnesota,  one  and  a  half  to  two 
and  a  half  feet  in  Dakota  and  Montana,  and  from  one 
to  two  feet  in  Wyoming  and  Nebraska.  On  the  Sierra 
Nevada  the  average  ranges  from  ten  to  thirty  feet. 

Among  the  remarkable  snowfalls  in  extreme  southern 
latitudes  may  be  mentioned  the  storm  of  January  12th 
-15th,  1882,  in  the  South  Pacific  coast  region,  when,  in 
California,  at  Los  Angeles,  the  hills  about  the  city  were 
white  with  snow,  five  inches  fell  at  Riverside,  three 
feet  at  Campo,  and  from  four  to  fifteen  inches  from 
San  Bernardino  eastward  to  the  edge  of  the  Mohave 
Desert,  and  at  a  short  distance  inland  from  San 
Diego.  The  snow  extended  on  the  low  hills  in  that 
region  far  southward  into  Lower  California,  Mexico 
(being  twenty  inches  deep  on  the  frontier),  and  in 
Arizona  very  heavy  snow  fell  upon  the  desert  to  the 
westward  of  Tucson.  It  is  probable  that  snow  falls  in 
these  low  latitudes  only  at  very  long  intervals,  since  a 
similar  storm  has  not  been  noted  in  those  sections  for 
nearly  fifty  years. 

On  January  27th-28th,  1880,  in  California  snow  fell 
at  Gonzales  for  the  first  time  in  ten  years  ;  at  Salinas 
for  the  first  time  on  record  in  the  Salinas  Valley  ;  at 


*  The  snowfall  in  single  years  very  largely  exceeds  the  average.     At 
North  Volney,  N.  Y.,  185  inches  are  reported  to  have  fallen  in  1856. 


AMERICAN   WEATHER.  161 

Los  Angeles  the  heaviest  ever  known  and  for  the  first 
time  in  fourteen  years,  and  through  all  Southern  Ari- 
zona the  snow  was  very  heavy,  with  high  winds. 

On  December  29th-31st,  1880,  unusually  heavy  snow 
fell  on  the  coast  region  bordering  the  Gulf  of  Mexico. 
There  was  five  inches  of  snow  at  Montgomery,  Ala., 
the  most  ever  known,  and  nearly  two  inches  at  Rio 
Grande  City,  Tex.,  the  first  since  December,  1866. 

A  somewhat  similar  storm  occurred  December  5th, 

1886,  when  snow  fell  in   considerable  quantities  at 
Charleston,  Savannah,  Mobile,  and  at  Pensacola,  F]a. 
Heavy  snow,  to  the  extent  of  about  four  inches,  fell  at 
New  Orleans  in  1852,  in  March,  1867,   and  January, 
1881.     At  Shelby ville,  Tenn.,  snow  fell  May  15th -16th, 
1843,  to  the  extent  of  fourteen  inches. 

The  following  are  among  the  most  remarkable 
monthly  snowfalls  in  the  United  States,  and  from  them 
may  be  fairly  estimated  the  quantity  of  snow  which 
may  be  called  extreme  during  any  month  : 

Cisco,  CaL,  March,  1882,  251  inches,  and  February, 

1887,  228  inches ;    Truckee,   JSTev.,   March,  1882,    120 
inches,  and  Fort  McDermit,  JSTev.,  January,  1885,  52.5 
inches,;    Palermo,  N".  Y.,  December,  1868,  sixty-eight 
inches ;    Marquette,    Mich.,    December,    1884,    sixty- 
seven  inches  ;   Eola,  Ore.,  December,  1884,  sixty-one 
inches ;    Straff ord,    Vt.,    February,    1887,     sixty-one 
inches  ;  Port  Angeles,  Wash.   Terr.,   February,  1887, 
forty-nine  inches  ;  Eockford,  111.,  March,  1887,  forty- 
seven  inches  ;  Worcester,  Mass.,  January,  1882,  fifty- 
three  inches  ;  Quincy,  IS".  JL,  February,  1887,  fifty-one 
inches  ;  Wauseon,  O.,  March,  1877,  41.7  inches  ;  Vir- 
ginia City,  Mont.,  December,  1879,  38.5  inches  ;  Cor- 
nish,  Me.  (in  the  woods),  February,  1887,  forty-eight 
inches  ;    Duluth,  Minn.,  December,   1879,  thirty-nine 
inches  ;  Greeneville,  Pa.,    December,  1886,    thirty-six 


162  AMERICAN  WEATHER. 

inches  ;  Beloit,  Wis.,  February,  1881,  forty-two  inches  ; 
South  Orange,  N.  J.,  December,  1872,  thirty-eight 
inches  ;  North  Colebrook,  Conn.,  December,  1886,  38.5 
inches  ;  Dover,  Del.,  and  Deer  Park,  Md.,  December, 
1880,  thirty-five  inches  ;  Mount  Solon,  Va.,  December, 
1880,  twenty-eight  inches  ;  Highlands,  N.  C.,  Decem- 
ber, 1880,  seventeen  inches  ;  Montgomery,  Ala.,  De- 
cember, 1885,  eleven  inches. 

Far  the  greater  part  of  the  snow  falls  from  December 
to  March,  but  occasionally  heavy  snowfalls  are  experi- 
enced in  the  northern  sections  of  the  United  States 
during  April  and  May.  Even  in  June  occasional  light 
snowfalls  have  occurred,  among  which  may  be  noted  a 
general  storm  in  Colorado,  June  8th,  1884,  and  falls  at 
Lynchburg,  Va.,  June  12th,  1887,  and  June  llth,  1857. 
Near  the  end  of  July,  1883,  snow  is  said  to  have  fallen 
at  Colebrook,  Coos  County,  N".  H. 

Probably  the  most  remarkable  July  snowfalls  ever 
recorded  are  those  of  1888,  which  were  experienced  in 
both  the  eastern  and  western  hemispheres. 

On  the  night  of  July  llth,  1888,  slight  falls  of  snow 
occurred  locally  over  Great  Britain,  even  as  far  south 
as  the  Isle  of  Wight  in  the  English  Channel.  The  day 
following  heavy  snow  fell  on  Mt.  Washington,  N.  H., 
reaching  nearly  to  the  base  of  the  mountain. 


CHAPTER  XII. 

THE  WINDS   OF  THE  UNITED   STATES. 

THE  classification  of  winds  by  Dove  into  permanent, 
periodical,  and  variable  has  much,  to  commend  it. 

The  northeast  and  southeast  trades  of  the  Atlantic 
Ocean  are  the  best  known  of  all  the  permanent  winds. 
They  are  separated  by  a  belt  of  calms,  from  four  to 
eight  degrees  wide,  which  always  remains  north  of  the 
equator.  For  about  twenty  degrees  of  latitude  to  the 
north  of  this  belt  the  wind  blows  almost  without  inter- 
ruption from  the  northeast.  The  trades  follow  the  sun 
northward  and  south  ward,  lagging  in  the  extreme  phases 
of  motion  about  a  month  behind  it.  It  must  be  admit- 
ted that  the  steadiness  of  the  trades  as  to  force  and  di- 
rection is  not  as  constant  as  once  set  forth.  Variations 
of  direction  and  interruptions  are  not  unusual  in  the 
open  ocean,  and  such  modifications  are  quite  decided 
near  land. 

The  middle  latitudes  of  both  hemispheres,  from  about 
the  30th  to  the  50th  parallels,  have  the  anti-trades,  per- 
manent westerly  winds,  which  in  the  Northern  Hemi- 
sphere are  materially  modified  on  land  by  local  and 
accidental  causes. 

The  most  important  periodical  winds  are  the  winter 
and  summer  monsoons  of  Southern  Asia,  where  from 
October  to  April  the  wind  blows  steadily  from  the 
northwest,  and  from  April  to  October  from  the  south- 
west. This  periodical  system  extends  from  about 
thirty  degrees  north  latitude,  in  Asia,  southward  to 
Northern  Australia, 


164  AMERICAN  WEATHER. 

The  interruption  attendant  on  the  reversal  of  the 
monsoon  is  called  the  "  bursting  of  the  monsoon," 
which,  both  in  May  and  October,  is  often  marked  by 
violent  hurricanes. 

The  term  monsoon  has  been  broadened  in  its  mean- 
ing, so  that  monsoon  winds  signify  those  which  recur 
with  returning  seasons.  The  attempt  to  apply  the  defi- 
nite term  monsoon  to  wind  systems  of  other  regions 
than  Southern  Asia  has  not  gained  general  consent, 
and  the  author  cannot  agree  with  those  who  credit  the 
United  States  with  monsoonal  winds. 

The  prevailing  surface  winds  of  the  greater  part  of 
the  United  States  are  from  southwest  to  northwest, 
and  so  are  in  substantial  harmony  with  the  upper  wind 
currents,  as  shown  by  Mount  Washington  (N.  W.),  ele- 
vation, 6279  feet,  and  Pike's  Peak  (S.  W.),  14,134  feet. 
The  mean  direction  toward  which  the  wind  blows  in 
the  United  States  would  not  differ  much  from  the  aver- 
age course  of  ordinary  low-area  storms — a  little  to  the 
north  of  east. 

South  of  the  31st  parallel  an  opposite  air  current  ob- 
tains, and  in  Florida  the  prevailing  winds  partake  of 
the  character  of  the  northeast  trades,  being  either  east- 
erly or  northeasterly  on  the  Florida  coast,  but  as  soon 
as  they  pass  into  the  Gulf  of  Mexico  and  reach  the 
land  they  veer  to  southeasterly  or  southerly.  In  this 
instance  also  it  is  to  be  remarked  that  the  path  fol- 
lowed by  the  wind  is  a  parabolic  one  closely  in  accord 
with  the  course  of  the  cyclonic  (hurricane)  storms  of 
the  Caribbean  Sea.  This  relation  of  wind  direction  to 
the  course  of  storms  is  worthy  of  note. 

The  passage  eastward  of  storms  developing  in  Sas- 
katchewan, or  along  the  eastern  Rocky  Mountain 
slope,  naturally  and  fortunately  tends  to  draw  north- 
ward the  moist  winds  of  the  Gfulf .  The  presence  of  the 


AMERICAN   WEATHER.  165 

Rocky  Mountain  range  aids  in  giving  these  winds  a 
westerly  component,  and  the  slow  rise  in  elevation  not 
only  gradually  affects  the  course  of  the  wind,  but  also 
condenses  the  moisture  slowly,  and  so  gives  rain  in 
sufficient  quantity  and  with  such  equability  as  to 
make  fruitful  millions  of  acres  of  arable  land,  instead 
of  pouring  down  torrents  and  drowning  out  a  narrow 
fringe  of  coast  region. 

The  prevailing  winds  to  the  eastward  of  the  Missis- 
sippi River,  excepting  the  Gulf  States,  are  generally 
southwest  to  northwest.  As  exceptions  may  be  men- 
tioned the  tendency  during  the  summer  months  for 
winds,  from  Maine  as  far  as  Virginia  to  back  to  south- 
erly, and  from  Virginia  to  Florida,  to  shift  to  north- 
easterly during  autumn. 

In  the  States  bordering  on  the  Gulf  of  Mexico  the 
winds  are,  as  a  rule,  from  the  south  or  southeast,  al- 
though in  winter  there  is  a  strong  tendency  in  Texas 
for  winds  to  shift  to  northerly.  The  Upper  Missis- 
sippi and  the  Missouri  Valley  regions  have  winds  ac- 
cording closely  with  the  south  or  southeasterly  winds 
of  the  Gulf  States,  except  that  in  winter  the  southerly 
winds  alternate  with  the  northwesterly,  the  latter 
winds  being  somewhat  more  frequent. 

Along  the  Rocky  Mountain  slope  the  winds  of  the 
northern  portion  are  decidedly  from  the  southwest, 
but  elsewhere  more  frequently  divided  between  two 
diametrically  opposite  points — south  and  north.  The 
frequent  development  of  low  areas  in  Saskatchewan 
induce  the  former  winds,  while  the  movement  of  high 
areas  southward  from  the  same  region  produce  winds 
from  the  opposite  quarter. 

In  the  Pacific  coast  region  the  country  is  so  broken 
and  of  such  constantly  varying  elevation  that  winds 
are  largely  local.  The  predominating  coast  winds  are 


166  AMERICAN   WEATHER. 

westerly,  while  inland  the  tendency  is  to  southerly 
breezes. 

The  United  States,  in  certain  districts,  are  also  liable 
to  dry,  hot  winds,  which  have  at  times  an  important 
effect  on  the  weather  in  producing  for  their  localities 
prolonged  periods  of  dry  weather,  known  as  hot  terms. 
The  best  known  of  these  are  the  easterly  winds  which 
blow  from  the  interior  of  California  toward  the  Pacific 
Ocean,  and  which  in  Southern  California  are  known 
as  the  desert  winds.  Winds  of  like  characteristics  are 
experienced  in  northeastern  Dakota  along  the  Mis- 
souri River,  where  they  blow  from  the  bad  lands  situ- 
ated to  the  south  or  southwest.  Similar  to  these  are 
the  scirocco  winds  of  the  African  coast,  which  come 
from  the  African  deserts,  and  which  reaching  Spain 
as  southeasterly  are  there  known  as  the  leveche.  In 
Egypt  the  desert  wind  is  popularly  supposed  to  blow 
for  fifty  days,  and  is  consequently  called  Khamsin. 
On  the  West  African  coast  this  desert  wind  is  known  as 
Harmattan. 

Apart  from  these  dry,  hot  winds,  which  come  from 
the  land,  should  be  mentioned  another  special  class, 
known  as  the  Foelin  winds.  This  wind,  first  studied 
and  explained  in  Switzerland  by  Hann,  where  it  is 
.called  the  FoeTin,  gives  its  name  to  similarly  heated 
winds  in  other  parts  of  the  world. 

The  warm  winds  to  the  eastward  of  the  Cascade 
range,  in  Idaho,  Washington,  and  Montana  territories, 
known  as  the  Chinook  winds,  are  in  part  Foehn  winds. 
In  a  like  manner  these  winds  occur  occasionally  to 
the  westward  of  Greenland,  and  under  favorable  con- 
ditions in  South  Africa,  Australia,  New  Zealand,  and 
Peru.  It  doubtless  occurs  that  in  many  cases  in  the 
United  States  these  cJiinook  winds  are  brought  by  at- 
mospheric circulation  from  a  more  southern  and  warmer 


AMEBlCAff   WEATHEB.  167 

region,  and  retain  in  their  northerly  course  a  portion 
of  their  original  heat,  but  in  general  their  abnormally 
high  temperature  is  to  be  attributed  to  similar  causes 
which  induce  it  in  the  Foehn  winds. 

Dry  air  in  passing  over  a  mountain  range  would  not 
differ  in  temperature  on  the  two  sides  of  the  range. 
As  the  air  ascended  it  would  be  cooled  dynamically. 
As  it  descended  it  would  be  warmed  just  as  much. 
But  if  the  air  is  moist,  in  ascending  it  cools,  and  the 
moisture  is  condensed  and  falls  as  rain.  The  latent 
heat  released  by  the  condensation  raises  the  tempera- 
ture of  the  air,  and  in  descending  the  other  side  of  the 
mountain  it  is  warmed  up  dynamically  still  more. 
This  is  the  action  of  the  Foehn  wind  and  the  explana- 
tion of  its  warmth  and  dryness. 

The  northers  of  the  United  States  are  dry,  cold, 
strong  winds  from  the  north,  which  are  generally  pre- 
ceded by  high,  warm  southerly  winds.  Similar  dis- 
agreeable and  violent  cold  winds  are  experienced  in 
many  other  regions,  all  resulting  from  abnormal  dis- 
tribution of  atmospheric  pressure.  Among  these  may 
be  mentioned  the  well-known  mistral,  a  northwest 
wind  which  blows  from  Eastern  and  Central  France 
down  on  the  Mediterranean  along  the  Riviera ;  the 
northeasterly  gregale  of  Malta,  the  northerly  tramon- 
tana  of  the  Adriatic,  and  bora  of  Trieste  and  Dalmatia. 

The  norther,  when  violent  and  the  air  is  filled  with 
drifting  snow,  is  known  in  the  United  States  as  a  bliz- 
zard, in  the  Yenisei  Valley  as  the  purga,  and  on  the 
steppes  of  Central  Asia  as  the  bur  a. 

In  the  Southern  Hemisphere  the  southerly  buster 
occurs  in  New  Zealand.  The  southwesterly  pampero 
in  Uruguay  and  the  southeast  winds  on  the  Punos  are 
also  cold  dry  winds  of  similar  origin. 

The  prevailing  direction  of  the  wind  does  not  abso- 


168 


AMEKICAN   WEATHER. 


lutely  show  the  actual  movement  of  the  atmosphere  at 
the  station,  since  winds  blow  with  variable  force.     An 


Average  Tvind  travel  at  \\itshingtonBC 


1884-1887 


FIG.  36. 


examination  of  the  records  of  wind  direction  and  ve- 
locity for  Washington  City  for  the  four  years  ending 


AMERICAN  WEATHER.  169 

December  31st,  1887,  gives  data  for  separating  the  ac- 
tual miles  of  wind  from  the  eight  principal  points  of 
the  compass,  which  appear  in  Fig.  26  in  percentages, 
thus  showing  the  wind's  translation  proportionally  for 
each  month.  It  appears  that  although  the  northwest 
wind  blows  but  twenty- two  per  centum  of  the  time, 
yet  31.1  per  centum  of  the  entire  wind  comes  from  that 
quarter,  which,  with  15.6  per  centum  from  the  north, 
shows  that  very  nearly  one  half  of  the  entire  miles  of 
wind  come  from  these  two  directions — north  and  north- 
west. The  south  winds  prevail  in  mileage  at  Washing- 
ton, as  will  be  seen,  only  from  May  to  September,  in- 
clusive, and  in  the  yearly  aggregate  only  17.2  per  cen- 
tum of  the  wind's  mileage  and  twenty  per  centum  of 
its  frequency  are  from  the  south.  The  northeast  wind 
approaches  the  south  in  percentage  in  June  and  the 
north  wind  in  August  and  September,  while  the  north- 
west is  only  slightly  less  than  the  south  in  any  sum- 
mer month,  so  that  no  summer  wind  is  monsoonal  in 
its  predominance.  The  number  of  miles  from  either 
the  east  or  the  southeast  is  so  small  and  differ  so  im- 
materially from  each  other  that  they  were  consoli- 
dated, each  comprising  about  five  per  centum  of  the 
wind  translation  at  Washington. 

The  average  velocity  in  miles  per  hour  of  the  wind 
from  the  different  quarters,  determined  from  these  four 
years'  observations  at  Washington,  is  as  follows : 
North,  5.7  ;  northeast,  5.2  ;  east,  4.6  ;  southeast,  4.7  ; 
south,  4.8  ;  southwest,  5.1  ;  west,  4.9  ;  northwest,  8.6. 

Put  forth  as  a  general  statement,  it  may  be  said  that 
for  the  United  States  the  monthly  period  of  wind  ve- 
locity finds  its  maximum  in  March  or  April  and  its 
minimum  in  August. 

As  given  by  Scott  for  Armagh,  Ireland  ;  Liverpool, 
England  ;  and  Sandwick,  Orkney,  the  maximum  and 


170  AMERICAN   \VEATI1EH. 

minimum  wind  phases  for  Great  Britain  seem  to  fall 
respectively  in  January  or  February  and  in  June  or 
July. 

Previous  to  the  use  of  self -registering  anemometers, 
it  was  only  known  that  winter  and  spring  winds  were 
usually  higher  than  those  of  summer  and  autumn. 
Records  of  the  past  ten  years  show,  as  a  general  rule, 
that  for  the  United  States  the  mean  monthly  wind 
velocity,  when  charted  for  the  year,  is  expressed  by  a 
curve  with  a  single  inflection,  the  decrease  to  the  low- 
est, and  increase  to  highest  being  regular  and  un- 
broken. 

The  average  velocity  of  the  wind  varies  quite  materi- 
ally from  month  to  month,  the  highest  mean  monthly 
velocity  at  any  place  averaging  for  the  United  States, 
as  a  whole,  about  fifty  per  centum  above  the  least. 
The  differences  are  greater  at  coast  stations  than  in- 
land, as  can  be  seen  from  Fig.  27.  Both  San  Francisco 
and  Eastport  experience  one  hundred  per  centum  more 
of  wind  in  the  maximum  month  than  in  that  of  the 
least  velocity.  For  the  greater  part  of  the  country  the 
average  velocity  of  summer  winds  is  between  five  and 
eight  miles  per  hour,  which  increases  from  December 
to  March  to  velocities  between  eight  and  twelve  miles 
hourly. 

The  following  figure,  No.  27,  shows  the  fluctuations 
through  the  year  of  the  mean  monthly  velocity  of  the 
wind  for  Eastport,  Me.  ;  New  York  City  ;  Cincinnati, 
O.  ;  Nashville,  Tenn.  ;  Dodge  City,  Kan.  ;  San  Fran- 
cisco, and  San  Diego,  Cal. 

In  the  United  States,  eastward  of  the  Mississippi, 
the  highest  mean  velocity,  generally  speaking,  occurs 
in  March,  as  shown  by  the  curves  for  Eastport,  New 
York,  and  Cincinnati,  while  to  the  westward  it  most 
frequently  obtains  in  April.  There  are  some  local  ex- 


AMERICAN   WEATHEli. 


171 


Average  hourly  velocity  of  the  wind  in  miles* 

Stations 

$ 

I  a 

\  i 

1  4 

*  4 

r  i 

i  * 

r  ^ 

f   A 

t  * 

!    ii 

\       % 

t~ 

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^=^ 

^^ 

v  •    "  •"  - 

> 

^ 

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/  . 

.-^ 

Nashville  

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FIG.   27. 

ceptions  to  this  rule,  the  most  marked  being  the  high 
winds  of  November  and  December  at  certain  stations 
on  the  great  lakes.  In  the  Pacific  coast  region  the 
winds  are  not  quite  so  regular,  being  highest  during 
January  and  February  on  the  north  Pacific  coast,  and 
in  June  and  July  on  the  middle  Pacific,  as  is  shown 
by  the  curve  for  San  Francisco. 

The  lowest  monthly  velocity  to  the  eastward  of  the 
Rocky  Mountains  occurs  in  August,  with  but  few  ex- 
ceptions. To  the  westward  of  the  mountains,  save 


172  AMERICAN  WEATHER. 

along  the  Washington  and  Oregon  coast,  the  least  wind 
is  in  November  or  December. 

The  wind  movements  for  the  whole  year  are  smallest 
at  places  in  the  Ohio  Valley,  in  the  interior  of  the 
south  Atlantic  and  eastern  Gulf  States,  in  Arkansas, 
Idaho,  Southern  California,  and  in  the  interior  of  Oregon 
and  Washington  Territory,  the  average  hourly  move- 
ment being  less  than  six  miles  in  the  above-mentioned 
regions.  The  lowest  annual  averages  are  those  of 
Nashville,  Tenn.  ;  Augusta,  Ga.,  and  Olympia,  Wash. 
Terr. — four  miles;  Roseburg,  Ore.,  and  Lewiston,  Ida. 
— three  miles. 

The  most  wind  for  the  year  prevails  at  exposed  sta- 
tions on  the  New  Jersey,  North  Carolina,  Texas,  and 
north  Pacific  coasts,  and  on  the  Rocky  Mountain  slope 
from  Eastern  Montana  to  Northern  Texas.  Annual 
average  velocities  ranging  from  eleven  to  seventeen 
miles  per  hour  obtain  at  such  stations.  Among  the 
highest  averages  are  those  for  Fort  Maginnis,  eleven 
miles  ;  Dodge  City,  Kan.,  and  Tatoosh  Island,  Wash. 
Terr.,  twelve  ;  Indianola,  Tex.,  and  Sandusky,  0., 
thirteen  ;  Sandy  Hook,  N.  J.,  fourteen  ;  Block  Island, 
R.  L,  and  Kitty  Hawk,  N.  C.,  fifteen ;  Delaware 
Breakwater,  Del.,  sixteen,  and  Cape  Mendocino,  Cal., 
17  miles.  The  exceptionally  high  velocities  of  this 
last  station  are  due  to  its  situation  on  very  high  land, 
637  feet,  directly  overlooking  the  ocean. 

The  highest  winds  occur  along  the  sea-coasts  and  lake 
shores,  whence  the  velocity  diminishes  inland  quite 
rapidly  as  the  distance  from  the  sea  increases.  One 
notable  exception,  perhaps  the  most  remarkable  in  the 
world,  is  the  wind  system  of  the  region  extending 
southward  from  Eastern  Dakota  to  Northern  Texas, 
over  which  exceedingly  strong  winds  prevail  both  sum- 
mer and  winter.  This  is  explained  by  the  physical 


AMERICAN  WEATHEK.  173 

configuration  of  the  country,  a  uniformly  descending 
plain,  sparsely  covered  with  vegetation  and  unbroken 
by  mountains  or  even  high  hills  for  a  thousand  miles, 
from  Montana  to  the  Gulf  of  Mexico.  The  Ozark  and 
other  small  mountain  ranges  partly  protect  Missouri 
and  Arkansas,  by  diverting  to  the  westward  both  the 
warm  southern  cyclonic  winds  from  the  Gulf  of  Mexico 
and  the  cold  outpours  of  cold  air  from  Saskatchewan 
or  Manitoba. 

In  Fig.  28  is  shown  the  mean  relative  velocity  of  the 
wind  for  each  hour  of  the  day  for  March,  as  determined 
from  four  years'  observations  at  important  points  in 
the  United  States.  This  month  is  selected  as  a  charac- 
teristic one,  since  its  mean  hourly  velocity  is  greater, 
as  a  rule,  for  the  United  States  than  that  of  any  other 
month.  Almost  without  exception  the  highest  mean 
velocity  occurs  at  2  or  3  P.M. — that  is  about  the  hour  of 
the  highest  temperature  of  the  day.  The  lowest  hourly 
velocity  obtains  at  hours  varying  from  4  A.M.  to  6  A.M. 
But  in  certain  localities  there  are  marked  exceptions 
to  this  rule.  For  instance,  at  Cheyenne  the  wind 
reaches  its  minimum  at  10  P.M.,  and  increases  steadily 
to  a  maximum  at  1  P.M.  At  Atlanta,  Augusta,  Chat- 
tanooga, and  Charleston  the  least  wind  occurs  about 
7  A.M.  If,  as  appears  strikingly  evident  from  Figs.  20 
and  28,  the  velocity  of  the  wind  largely  depends  on 
the  ascending  or  descending  currents  set  in  motion  by 
the  heating  of  the  air  or  radiation  of  the  earth,  it 
would  be  expected  that  the  hours  for  the  least  wind 
would  be  somewhat  indefinite. 

A  very  marked  exception  to  this  rule  is  shown  by 
the  records  at  Block  Island,  an  island  off  the  coast  of 
Rhode  Island,  where  general  inflection  of  the  curve,  as 
will  be  seen,  is  in  direct  opposition  to  the  land  curves, 
the  maximum  obtaining  at  5  A.M.  and  the  minimum 


174 


AMERICAN  WEATHEK. 


AM: 


M: 


EM: 


vl    23*56  17  89  10  11  12  123*56789  10  11 12 


IS 


13 


\ 


Cfilcaga- 


%& 


K 


Briton^ 
Qregori*. 


FIG.   28. 

from  noon  to  5  P.M.  Nearly  the  same  thing  occurs  at 
Thunder  Bay  Island,  Lake  Huron,  where  the  maximum 
occurs  at  2.30  A.M.  This  may  be  a  climatic  characteris- 
tic of  islands  near  mainland. 

The  regularity  with  which  the  mean  hourly  velocity 


AMERICAN   WEATHEK.  175 

of  the  wind  follows  the  mean  hourly  temperature  of 
the  air  is  strikingly  evident  by  comparison  of  Figs.  20 
and  28.  The  variation  in  the  mean  velocity  of  the 
wind  from  hour  to  hour  is  very  great,  since,  as  a  rule, 
the  velocity  is  from  forty  to  seventy  per  centum  greater 
at  the  hour  of  its  maximum  than  at  the  hour  of  least 
velocity.  At  certain  stations  where  the  mean  wind 
velocity  is  small,  the  increase  is  even  greater,  being  in 
some  localities  over  one  hundred  per  centum,  as  is 
shown  by  the  curve  for  Portland,  Ore. 

During  the  winter  months  the  wind,  as  has  been 
pointed  out,  is  of  greater  velocity  than  in  the  summer 
months,  and  occasionally  the  mean  hourly  velocity  of 
the  wind  for  an  entire  month  has  been  excessively 
great.  Among  the  most  striking  instances  which  will 
serve  to  illustrate  the  excessive  phase  of  this  phenom- 
enon in  the  United  States  are  the  following :  Mount 
Washington  (elevation,  6279  feet),  during  January,  1885, 
the  mean  hourly  velocity  was  forty --nine  miles  per  hour 
throughout  the  month,  and  in  February,  1883,  forty- 
eight  miles ;  Pike' s  Peak  (elevation,  14, 134  feet),  Decem- 
ber, 1886,  thirty-two  miles  ;  Cape  Mendocino  (elevation, 
637  feet),  November,  1885,  twenty-nine  miles  ;  Sandy 
Hook,  December,  1885,  and  Cape  May,  March,  1887, 
twenty-two  miles  ;  Cape  Hatteras,  March,  1883,  twenty 
miles  ;  Tatoosh  Island,  January,  1886,  nineteen  miles  ; 
Fort  Shaw,  Mont.,  February,  1882,  eighteen  miles  ; 
Cheyenne,  Wyo.,  February,  1886,  Rochester,  N.  Y., 
February,  1883,  and  Dodge  City,  Kan.,  March,  1884, 
seventeen  miles  per  hour  for  the  entire  month. 

In  marked  contrast  to  these  excessive  velocities  for 
long  periods  is  instanced  the  wind  movement  at  Lewis- 
ton,  Ida.,  for  November,  1884,  when  the  velocity  was 
but  0.4  miles  per  hour. 

As  very  remarkable  wind  storms  which  lasted  for 


176  AMERICAN  WEATHER. 

long  periods  may  be  quoted  that  of  Mount  Washing- 
ton, February  27th,  1886,  when  the  mean  hourly  veloc- 
ity for  twenty-four  hours  was  111  miles,  and  at  Yank- 
ton,  Dak.,  April  13th,  1873,  when  the  mean  hourly  ve- 
locity for  the  twenty-four  hours  was  about  fifty  miles. 
The  maximum  velocity  of  the  wind  in  the  Signal 
Service  has  been  usually  obtained  from  the  rate  for 
fifteen  consecutive  minutes,  and  the  following  extreme 
velocities  referred  to  have  been  determined  in  like 
manner :  By  'this  method  it  appears  that  the  highest 
winds  ever  recorded  are,  as  a  rule,  between  the  limits 
of  fifty  miles  per  hour  and  seventy  miles  per  hour  for 
the  sections  of  the  United  States  between  the  Rocky 
Mountains  and  the  Atlantic  Ocean.  In  the  Rocky 
Mountain  districts  and  the  Pacific  coast  region  the 
velocity  has  very  rarely  exceeded  fifty  miles  an  hour. 
At  Cape  Mendocino  a  velocity  of  144  miles  was  reached 
January,  1886  ;  104  miles  at  Fort  Canby,  December, 
1884,  and  eighty-two  miles  at  Portland,  December 
12th,  1882.  The  highest  velocities  for  any  section  are 
those  experienced  along  the  middle  and  south  Atlantic 
coasts.  Winds  ranging  from  seventy  to  eighty  miles 
per  hour  have  been  occasionally  recorded  along  the 
whole  of  this  coast  line.  On  the  North  Carolina  coast 
velocities  ranging  from  ninety  to  a  hundred  miles 
have  several  times  occurred  during  cyclones  from  the 
West  Indies.  Among  the  most  remarkable  of  these 
velocities  may  be  quoted  Sandy  Hook,  Cape  May,  and 
Cape  Henry,  eighty -four  miles  ;  Fort  Macon,  ninety- 
two  ;  Southport,  ninety-eight ;  Kitty  Hawk  and  Cape 
Hatteras,  100  (the  latter  estimated) ;  Cape  Lookout, 
138  miles.  The  last-named  velocity  occurred  during 
the  great  hurricane  of  August  17th,  1879,  when  the 
anemometer  blew  away  before  the  wind  reached  its 
maximum  velocity. 


AMERICAN   WEATHER.  177 

On  the  summit  of  Pike's  Peak  the  extreme  velocity 
recorded  is  comparatively  low,  being  112  miles  in  June, 
1881.  Velocities  exceeding  this  have  not  been  infre- 
quent on  Mount  Washington  for  many  consecutive 
hours,  and  in  January,  1878,  the  extraordinary  velocity 
of  186  miles  per  hour  occurred. 

At  Montreal,  Can.,  on  March  13th,  1888,  the  wind 
blew  at  the  rate  of  110  miles  per  hour  for  a  single  mile, 
but  only  at  the  rate  of  ninety  for  three  miles — i.e.,  for 
a  period  of  two  minutes  only. 

The  velocity  of  gusts  which  have  occurred  during 
hurricanes  and  tornadoes  undoubtedly  exceed  100 
miles  an  hour,  and  possibly,  in  view  of  the  high  veloci- 
ties on  Mount  Washington,  m^y  even  reach  for  brief 
periods  the  rate  of  200  miles. 


CHAPTER  XIII. 

STORMS. 

THE  author  was  some  time  since  asked,  "  What  is  a 
storm  ?  What  do  you  mean  when  you  say  a  storm  is 
coming  ?' '  The  definition  then  given  may  serve  here. 
A  storm  is  a  decided  or  violent  disturbance  of  the  at- 
mosphere, which  undergoes  translation  from  place  to 
place.  This  disturbance  may  or  may  not  be  accom- 
panied by  precipitation,  such  as  snow  or  rain,  but  the 
area  of  disturbance  must  move  from  point  to  point, 
and  there  must  be  a  decided  transfer  of  air,  indicated 
either  by  strong  surface  winds  or  by  marked  changes  of 
pressure,  showing  upper  air  currents — silent,  but  none 
the  less  efficacious. 

Again,  this  atmospheric  commotion  may  be  general 
and  widespread,  the  storm-centre  travelling  for  days 
slowly  across  the  whole  country,  with  strong  winds  and 
moderate  long-continued  rain  ;  or  perchance  a  passing 
local  thunderstorm  with  lightning  and  hail,  which 
spends  its  force  within  narrow  limits  in  a  scant  hour's 
time  ;  or  it  may  be  a  violent  tornado  with  destructive 
winds  cutting  a  narrow  path  a  few  hundred  yards  wide 
and  a  mile  in  length,  its  coming  and  going  a  matter 
of  minutes.  The  main  distinguishing  feature  is  then 
the  movement  of  the  air — the  presence  of  wind.  In 
the  United  States  we  may  consider  as  a  storm  such  a 
disturbance  as  diverts  the  winds  to  a  marked  degree 
from  their  usual  direction,  while  augmenting  their  cus- 
tomary force.  As  has  been  pointed  out  in  the  chapter 


AMERICAN   WEATHER.  179 

on  winds,  the  force  of  the  wind  varies  largely  each  day, 
and  also  is  not  constant  for  different  months.  In  gen- 
eral, it  may  be  held  that  an  increase  in  velocity  twenty 
per  centum  above  the  mean  indicates  that  the  wind  is 
a  storm  wind.  Storm  winds  vary  from  200  to  300 
miles  daily  travel  with  freezing  temperatures,  or  300  to 
400  miles  at  higher  temperatures.  Winds  from  twenty 
to  thirty  miles  per  hour  are  considered  dangerous,  ac- 
cording to  the  degree  of  cold  and  the  amount  and  kind 
of  attendant  precipitation,  or  its  total  absence. 

The  severity  of  the  disturbance  is  not  always  evi- 
denced by  the  abnormally  high  or  low  reading  of  the 
barometer,  the  prevalence  and  amount  of  the  precipita- 
tion, nor  even  by  the  violence  of  the  winds — although 
this  latter  is  generally  a  good  index — but  by  the  baro- 
metric gradient.  This  gradient  indicates  the  change 
of  barometric  pressure  in  a  given  distance,  and  has  at 
its  unit  of  pressure  .01  inch,  and  of  distance  fifteen 
geographical  miles,  measured  perpendicular  to  the 
isobars. 

As,  for  instance,  a  gradient  of  two  means  that  under 
such  condition  in  a  distance  of  fifteen  miles  there  is  a 
difference  of  two  hundredths  of  an  inch  between  the 
reduced  readings  of  two  barometers. 

It  seems  advisable  that  a  thermometric  gradient 
should  be  formulated,  since  it  is  a  marked  feature  of 
certain  strong,  cold  winds  that  they  appear  to  depend 
almost  entirely  on  difference  of  temperature  in  a  given 
distance,  as  they  occur  with  very  feeble  barometric 
gradients.  It  is  suggested  that  the  unit  of  such  a 
gradient  be  one- tenth  of  a  degree  to  a  distance  of  a 
degree  of  a  great  circle  on  the  earth's  surface,  which  is 
sixty  geographical  miles. 

The  winds  are,  as  a  rule,  proportional  to  the  steep- 
ness of  the  gradient,  and  the  tendency  of  cyclonic 


180  AMEKICATST   WEATHER. 

winds  is  spirally  inward  and  upward  toward  the  centre 
of  barometric  depression,  the  circulation  being  con- 
trary to  the  motion  of  the  hands  of  a  watch.* 

Atmospheric  disturbances  are  easily  divided  into  two 
classes — cyclonic  or  low-area  storms  and  anti-cyclonic 
or  high-area  storms. 

By  a  cyclonic  storm  is  not  necessarily  meant  a 
cyclone  or  hurricane,  but  a  storm  characterized  by  an 
atmospheric  pressure  below  the  average,  and  having  a 
wind  system  blowing  spirally  inward,  as  do  the  winds 
of  a  genuine  cyclone. 

The  causes  which  bring  about  a  cyclonic  or  low-area 
storm  are  not  fully  and  accurately  known.  That  they 
result  from  the  action  of  the  sun  in  disturbing  the 
general  atmospheric  equilibrium,  by  causing  variations 
in  the  density  of  the  air,  is  admitted,  but  beyond  this 
opinion  diverse  theories  obtain,  and  it  is  not  probable 
the  problem  can  ever  be  resolved  with  positive  exact- 
ness. Although  far  the  greater  part  of  the  action  of 
all  and  the  whole  of  some  storms  takes  place  within 
a  mile  of  the  surface  of  the  earth,  yet  the  movement 
of  upper  clouds  and  occasional  attendant  peculiar 
phenomena  indicate  quite  clearly  that  the  origin  and 
most  important  phases  of  many  violent  atmospheric 
changes  must  be  assigned  to  the  upper  strata  of  the 
air.  It  is  well  known  that  the  abnormal  conditions 
which  characterize  low-area  storms  often  pass  by  Mount 
Washington  without  obtaining  on  its  summit  (6279 
feet),  and  that  low  mountain  ranges,  such  as  the  Alle- 
gheny or  Blue  Ridge,  occasionally  break  up  or  mate- 
rially modify  the  course  and  progress  of  such  storms. 

The  formation  of  a  depression  or  low  area  is  prob- 


*  This  applies  to  the  Northern  Hemisphere  only,  since  in  the  Southern 
Hemisphere  the  movement  is  with  the  hands  of  a  watch. 


Jeceniber 
torm  Chart 


total  rLu,7n,l>e7»ofslarm> 
jrsover  e&ck,  sqvcavre'. 


AMERICAN   WEATHER.  181 

ably  due  to  precipitation  or  formation  of  cloud,  or  is 
at  least  very  closely  related  in  some  way  to  the  con- 
densation of  aqueous  vapor.  The  motion  of  the  low 
area  probably  depends  on  the  prevailing  direction  of 
motion  of  the  great  body  of  upper  air  in  the  vicinity  of 
the  low.  A  current  of  air  on  the  earth's  surface,  no 
matter  in  what  direction,  is  deflected  to  the  right  hand 
of  the  direction  in  which  it  is  moving  in  the  Northern 
Hemisphere  by  the  action  of  the  rotation  of  the  earth. 
A  wind  moving  with  a  velocity  of  thirty  miles  an  hour 
from  south  to  north  in  latitude  40°  north,  for  instance, 
will  be  deflected  toward  the  east  six  miles  in  an  hour, 
neglecting  the  friction  of  the  wind  on  the  earth's  sur- 
face, the  effect  of  which  is  to  augment  considerably  the 
deflection. 

The  heavy  rainfalls  are  probably  the  initiating  and 
predominating  cause,  since  cyclones  of  the  Caribbean 
Sea,  with  attendant  excessive  precipitation,  develop 
into  severe  storms  before  the  deflecting  force  exerts 
any  considerable  influence.  Similar  results  are  evi- 
dently attendant  on  heavy  local  rainfalls  in  connection 
with  the  cyclones  of  the  Indian  Ocean.  Blanf ord  and 
Eliot  maintain  that  these  storms  are  consequent  on 
such  precipitation. 

It  again  occurs  that  two  high  areas  are  so  placed  in 
juxtaposition  that  the  outflow  of  air  tends  to  set  up  a 
cyclonic  wind  circulation  between  them,  when  the 
pressure  falls,  and  a  storm-centre  develops. 

The  largest  diameter  of  a  low-area  storm-centre  in  the 
United  States  extends  most  frequently  from  W.  S.  W. 
to  E.  K  E.,  although  its  direction  may  be  in  any 
azimuth.  This  shape  is  associated  with  the  frequent 
occurrence  of  high  or  anti-cyclonic  areas  both  to  the 
northwest  and  southeast  of  the  low  area,  causing  the 
gradients  on  these  sides  to  be  steepest  and  the  isobars 


182  AMERICAN  WEATHER. 

most  crowded  in  these  quadrants.  This  condition  is 
so  well  known  that  a  marked  elongation  of  the  storm- 
centre  in  the  northwest  part  of  the  United  States  or 
on  the  Atlantic  coast  is  held  to  indicate  an  excessive 
high  area  to  the  northwest  and  southeast,  respectively, 
beyond  the  limits  of  the  ordinary  weather  maps  in 
British  America  and  over  the  Atlantic  Ocean. 

Occasionally  the  isobars  surrounding  the  centre  of  a 
depression  are  circular,  but,  as  a  rule,  they  approach 
nearest  to  the  form  of  an  elongated  ellipse,  in  which 
the  diameter  of  the  longer  axis  is  from  1.3  to  2.5  greater 
than  the  shorter.  As  the  low  areas  pass  from  land  to 
sea  they  become  more  regular  in  shape,  the  elongation 
being  modified,  and  it  often  occurs  that  the  depression 
at  the  centre  becomes  more  marked,  with  a  correspond- 
ing steepness  of  gradient  and  increased  violence  of 
winds. 

The  reason  for  irregularity  of  form  in  isobars  on  land 
is  not  definitely  known,  but  since  they  disappear  in 
part  over  the  level  expanse  of  the  ocean,  it  is  not  un- 
reasonable to  suppose  that  these  irregularities  are  due 
in  large  part  to  the  physical  configuration  of  the  land 
over  which  they  pass.  The  broken  land  surfaces  mod- 
ify materially  the  precipitation,  and  thus  increase  or 
diminish  the  influence  of  an  important  factor  in  the 
storm's  progress — the  latent  heat  given  forth  by  the 
condensation  of  the  indrawn  vapor.  The  irregularity 
of  the  land  interferes  likewise  largely  with  the  free 
and  full  indraught  of  surface  winds,  which  thus  pre- 
vail unequally  in  different  quarters,  even  when  the 
gradient  is  uniform  on  all  sides. 

The  frequency  and  usual  tracks  of  low-area  storms 
in  the  Northern  Hemisphere  are  shown  on  Charts  XX. 
and  XXI.,  for  the  representative  months  of  August  and 
^December,  these  months  being  selected  as  being  re- 


August 
StormChart 


vterncdioTuil  Observalions\ 
18794886 


°s  show  iotai  number  of  storm, 
enters  over  eachsQuare. 


AMERICAN  WEATHER.  183 

spectively  the  least  and  most  stormy  for  this  hemi- 
sphere. In  the  centre  of  each  square  of  five  degrees  is 
entered  the  total  number  (if  six  or  more)  of  storm- 
centres  which  have  passed  over  any  part  of  the  square 
in  the  eight  years,  1879  to  1886,  inclusive.  It  appears 
that  the  valley  of  the  St.  Lawrence  has  the  largest 
number  of  storms  of  any  section  of  the  globe.  The 
greater  number  of  American  storms  originate  in  the 
Saskatchewan  country  or  on  the  southeastern  slope  of 
the  Rocky  Mountains.  A  minor  number  are  devel- 
oped in  the  Caribbean  Sea,  the  Gulf  of  Mexico,  or 
come  from  the  Pacific,  and  it  is  not  unusual  for  these  de- 
pressions to  be  broken  up  or  undergo  great  loss  of  energy 
in  crossing  the  Rocky  or  Appalachian  mountain  ranges. 

The  tendency  for  storms  to  follow  certain  routes 
or  to  diverge  therefrom  is  illustrated  by  the  solid 
track  lines  on  the  charts.  As  has  been  said,  the  ulti- 
mate course  of  low-area  storms  is  somewhat  north 
of  east.  As  most  noticeable  departures  from  this  rule 
may  be  mentioned  the  parabolic  course  of  cyclonic 
storms  (to  be  treated  of  later),  the  southward  direction 
of  storms  from  Manitoba  into  the  valley  of  the  Upper 
Mississippi,  from  Alaska  to  Oregon,  and  across  the 
Bay  of  Biscay  to  the  Mediterranean.  The  reason  for 
these  abnormal  paths  are  probably  the  heavy  rainfalls 
along  the  north  Pacific  coast  in  the  first  case,  and  in 
the  second  the  condensation,  as  cloud  or  rain,  of  the 
abundant  vapor  brought  into  the  valley  of  the  Missis- 
sippi by  southerly  winds  from  the  Gulf  of  Mexico,  as 
mentioned  on  page  164. 

Similar  reasons  obtain  in  the  third  case,  as  the  initi- 
atory divergence  of  the  storm-centre  to  the  southeast 
into  the  Bay  of  Biscay  is  always  marked  by  heavy 
rainfall,  ranging,  as  a  rule,  from  0.39  inch  at  Brest 
and  Bordeaux  to  0.48  inch  at  Madrid  and  0.94  inch 


184  AMERICAN   WEATHER. 

daily  at  Lisbon.  These  conditions  are  also  supple- 
mented by  a  secondary  cause,  since  at  such  times  a 
high  area  with  intervening  steep  gradients  prevails 
over  Sweden  and  Norway  to  the  northeast,  while  a  sec- 
ond high  area  is  to  the  southwest  over  the  middle 
Atlantic. 

In  general,  but  not  invariably,  land  storms  which 
travel  slowly  are  less  violent  than  those  which  move 
with  great  rapidity.  The  same  causes  that  lead  to  vio- 
lent fluctuations  and  increasing  intensity  near  the 
storm-centres  appear  to  favor  rapid  progression. 

The  number  of  well-defined  low-area  storms  which 
cross  the  United  States  average  eight  in  each  month, 
from  May  to  August,  inclusive  ;  nine  from  September 
to  November,  and  in  April ;  eleven  in  February,  March, 
and  December,  and  twelve  in  January. 

Storms  move  more  rapidly  in  the  United  States  than 
elsewhere.  The  most  rapid  progression  everywhere  is 
in  winter,  about  one  half  greater  than  in  summer. 
The  same  ratio,  it  may  be  remarked,  exists  between 
the  mean  velocity  of  summer  and  winter  winds  of  this 
country.  The  average  velocity  of  low-area  storms  in 
the  United  States  is  twenty-five  miles  per  hour  from 
June  to  September,  inclusive.  It  rises  gradually  to 
twenty-nine  miles  in  October,  thirty  in  November, 
thirty-five  in  December,  and  thirty-eight  in  January 
and  February,  whence  it  sinks  to  thirty-three  miles 
for  March  and  twenty-six  miles  per  hour  in  April 
and  May.  It  has  been  known  for  many  years  that  the 
velocity  of  winter  storms  is  greater  than  that  of  sum- 
mer, but  a  careful  examination  of  the  velocity  of 
storms  during  the  past  twelve  years  in  the  United 
States  shows  that  the  increase  is  regular  and  unbroken 
from  September  to  February,  and  thence  the  decrease 
is  regular  to  June. 


AMERICAN  WEATHER.  185 

It  follows,  then,  that  the  fluctuation  of  the  United 
States  storms  throughout  the  year,  as  to  frequency  and 
rapidity  of  movement,  is  accurately  represented  by  ap- 
proximately similar  curves,  which  have  but  a  single 
inflection,  with  the  maximum  frequency  and  rapidity 
in  January  and  February  and  the  minimum  from  May 
to  August  inclusive. 

The  movements  of  low  areas  in  middle  latitudes  to 
the  eastward  evidently  depend  on  the  general  drift  of 
the  atmosphere  in  that  direction.  As  has  been  pointed 
out  on  page  164,  the  general  direction  of  the  surface 
winds  does  not  differ  very  materially  from  the  general 
course  of  low-area  storms,  although  the  direction  of 
the  latter  is  apparently  affected  to  a  considerable  ex- 
tent by  the  trend  of  the  Ohio  and  St.  Lawrence  val- 
leys, followed  so  often  by  the  storm-centre. 

That  the  velocity  of  the  surface  winds  is  less  than 
that  at  which  storms  move  is  what  might  be  expected, 
since,  owing  to  friction  with  the  surface  of  the  earth, 
these  winds  blow  with  much  less  velocity  than  the 
upper  air  currents.  The  interruptions  of  the  regular 
westerly  winds  are  not  infrequent  near  the  surface  of 
the  earth,  but,  as  the  observations  on  Pike's  Peak  and 
Mount  Washington  show,  these  interruptions  are  rare 
and  of  short  continuance  in  the  upper  currents. 

The  hourly  velocities  of  the  wind  for  January  and 
July,  respectively,  at  these  high  stations  are  as  fol- 
lows :  Mount  Washington  (6279  feet),  about  forty-one 
and  twenty -nine  miles  ;  Pike's  Peak  (14,132  feet), 
twenty-five  and  twelve  miles.  The  mean  hourly  ve- 
locity of  low-area  storms  in  January  is  37.5  miles,  and 
in  July,  25.2  miles. 

It  thus  follows  that  the  mean  velocity  of  the  trans- 
ference of  storm  conditions  on  the  surface  of  the  earth 
is  not  far  from  being  equal  to  the  mean  movement  of 


186  AMERICAN  WEATHER. 

the  upper  currents,  as  deduced  from  the  observations 
on  these  two  high  and  widely  separated  peaks. 

The  mean  hourly  velocity  for  the  year  of  the  wind 
on  Mount  Washington  is  not  accurately  known,  owing 
to  large  accumulations  of  frost  on  the  anemometer 
during  certain  periods,  but  it  can  hardly  vary,  not 
more  than  a  mile  or  two,  from  thirty-four  miles  per 
hour — only  five  miles  greater  than  the  mean  hourly 
velocity  of  low-area  storms  ;  so  that  the  latter  appar- 
ently correspond  to  the  movement  of  upper  air  strata 
in  New  England  at  about  6000  feet. 

From  personal  investigation,  the  author  is  disposed  to 
go  further,  and  express  his  belief  that  the  average 
movement  of  low-area  storms,  at  least  in  the  United 
States  to  the  eastward  of  the  100th  meridian,  bears  a 
direct  relation  to  the  velocity  over  this  region  of  the 
upper  air  currents  at,  say,  6000  feet.  It  appears  in  this 
connection  also  more  than  probable  that  the  movement 
of  the  upper  currents  must  have  a  potent  influence  upon 
the  direction  of  motion  of  the  storm-centre,  although 
it  does  not  necessarily  follow  that  the  storm-centre 
should  move  exactly  in  the  same  direction  as  the  upper 
currents,  but  rather  there  should  be  deflections  depend- 
ent on  the  disturbing  effect  of  the  sun's  heat  upon 
the  regions  of  cloud,  and  also  through  the  effect  of  the 
daily  axial  rotation  of  the  earth.  In  support  of  this 
opinion  Fig.  29  is  presented,  which  shows  the  mean 
hourly  velocity  of  low- area  storms,  generally  those  to 
the  eastward  of  the  100th  meridian,  and  the  mean 
velocity  of  the  air  as  determined  from  observations 
from  1881-87  on  the  summit  of  Mount  Washington 
(6279  feet).  This  figure  shows  the  most  striking  ac- 
cord between  these  two  phenomena.  The  observations 
on  Mount  Washington  cannot  be  considered  as  abso- 
lutely correct,  owing  to  the  great  difficulty  of  securing 


AMERICAN  WEATHER. 


187 


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188  AMERICAN   WEATHER. 

continuous  registration  of  the  wind.  During  very 
many  days  of  the  year  the  accumulations  of  frost 
upon  the  anemometer  are  such  as  to  quite  materially 
reduce  the  velocity,  which  probably  for  some  months 
should  be  one  to  two  miles  greater  than  is  shown  in 
this  diagram.  On  the  other  hand,  there  appears  to  be 
little  doubt  but  that  the  anemometer  records  a  velocity 
too  great  by  eight  to  twelve  per  cent  at  velocities  be- 
tween twenty-five  and  forty  miles,  so  that  the  reduction 
of  the  anemometer  observations  to  a  standard  would 
undoubtedly  involve  a  greater  correction  than  the  loss 
through  frost-work  upon  the  anemometer.  In  such  a 
case  there  is  good  reason  for  believing  that,  after  proper 
corrections,  the  two  lines  would  be  more  closely  in 
accord  than  is  shown  in  the  present  diagram. 

An  examination  of  the  records  of  the  velocity  of  the 
wind  on  Mount  Washington  for  eighty  months  shows 
that  in  departures  from  the  normal  the  average  veloc- 
ity of  the  wind,  in  sixty  per  centum  of  the  months,  dif- 
fers five  miles  or  less  from  the  departures  in  the  ve- 
locity of  storm  areas,  and  that  in  fourteen  per  centum 
more  of  the  cases  the  differences  of  departure  are  be- 
tween five  and  one-tenth  miles  and  seven  miles.  Fur- 
ther, it  appears  that  in  fifty  per  centum  of  the  cases 
the  maxima  and  minima  monthly  velocities  of  storms 
and  upper  air  currents  are  in  accord,  representing  in 
identical  months  the  extremes  of  these  phases. 

It  not  infrequently  occurs  that  low-area  storms  pur- 
sue decidedly  abnormal  paths— i.e.,  toward  a  point  in 
the  western  quadrants— from  south  to  northwest. 
These  abnormal  movements  result  most  frequently  when 
in  the  abnormal  direction  occurs  predominating  rainfall, 
either  locally  heavy  or  widely  distributed,  or  when  the 
adjacent  high  areas  assume  such  relative  positions  that 
their  outflowing  currents  facilitate  the  inauguration  of 


AMERICA^  WEATHER.  189 

a  distinct  system  of  cyclonic  winds,  as  a  new  storm- 
centre. 

In  many  cases  this  abnormal  westerly  movement  is 
rather  apparent  than  real,  since  the  storm-centre  is 
either  retarded  and  coalesces  with  another,  or  its 
energy  is  being  gradually  dissipated.  In  either  case 
it  may  be  held  that  the  original  storm  vortex  is  de- 
stroyed, and  that  the  mere  fact  of  the  lowest  pressure 
being  found  to  the  westward  after  such  changes  does 
not  indicate  that  the  original  vortex  has  moved  in  that 
direction.  Doubtless,  too,  at  times  the  easterly  move- 
ments of  upper  air  currents  are  interrupted,  from  gen- 
eral and  widespread  disturbances  of  the  atmosphere 
quite  beyond  our  ken,  and  since  the  strata  into  which 
the  indraughted  air  passes  has  an  abnormal  movement, 
the  surface  conditions  undergo  a  corresponding  dis- 
placement. 

The  violent  low-area  storms  of  the  West  Indies, 
Southern  Indian  Ocean,  Bay  of  Bengal,  and  China 
Sea  have  peculiar  characteristics  which  place  them 
in  a  special  class.  Known  in  the  United  States  as 
cyclones  or  hurricanes  of  the  West  Indies,  they  are 
called  cyclones  in  India,  hurricanes  at  Mauritius,  and 
typhoons  in  the  China  Sea.  They  are  always  accom- 
panied by  heavy  and  frequently  by  torrential  rain, 
follow  parabolic  paths  (first  to  the  westward,  and  then 
to  the  north,  and  finally — unless,  passing  into  the  in- 
terior of  a  country,  the  storm  is  broken  up— to  the 
northeast),  have  limited  nearly  circular  areas,  sudden, 
sharp  falls  of  the  barometer,  steep  gradients,  violent 
winds,  and  a  slow  movement  of  translation.  About 
ninety  per  centum  of  the  cyclones  in  the  West  Indies 
occur  in  August,  September,  or  October.  In  Asiatic 
waters  these  storms  prevail  both  during  the  above- 
named  months  and  in  April,  May,  or  June,  being 


190  AMERICAN  WEATHER. 

most  frequent,  as  has  been  set  forth  on  page  164,  at 
the  "  bursting  of  the  monsoon."  The  storm  tendency 
is,  however,  considerably  greater  in  India  during  the 
autumnal  months  than  in  the  spring,  except  on  the 
Bombay  coast,  when  spring  cyclones  are  three  times  as 
frequent  as  those  of  autumn. 

The  cyclone,  if  of  smaller  extent  and  more  regular 
formation,  is  more  dangerous  than  ordinary  storms, 
owing  to  the  extreme  violence  and  sudden  shifting  of 
its  winds.  The  side  of  the  path  toward  which  the 
curvature  tends — the  right-hand  half  for  West  India 
storms — is  known  as  the  dangerous  quadrants.  This 
is  owing  to  the  continual  tendency  of  the  winds  of 
these  quadrants  to  carry  vessels  near  to  or  in  front  of 
the  centre— the  most  dangerous  position — so  that  a  ves- 
sel cannot  run  before  the  wind,  but  must  heave-to. 
The  other  quadrants  are  called  avoidable,  since  in  them 
a  vessel  can  be  put  before  the  wind,  and  thus  avoid  the 
central  vortex. 

As  has  been  long  since  pointed  out,  the  cold  winds 
following  in  the  wake  of  low  pressure  do  not,  near  the 
surface  of  the  earth,  blow  with  a  velocity  equal  to  the 
progress  of  the  storm-centre  itself,  and  some  comment 
has  been  made  as  to  this  being  an  inexplicable  phe- 
nomenon. It,  however,  appears  very  simple  of  expla- 
nation, for  it  is  well  known  that  upper  air  currents  move 
with  a  far  greater  velocity  than  do  the  surface  winds, 
and  there  is  no  doubt  but  that  these  upper  currents 
move  with  as  great,  or  possibly  even  greater,  velocity 
than  does  the  storm-centre  itself.  The  cold,  dry  air 
which  flows  in  behind  the  storm  at  the  surface  of  the 
earth  is  greatly  retarded  by  the  friction,  and  also  by 
the  fact  that,  when  retardation  through  friction  is  once 
inaugurated,  the  current  must  be  a  slightly  descend- 
ing one,  and  the  greater  the  retardation  the  sharper 


AMERICAN   WEATHER.  191 

will  be  the  curve  of  the  descending  air  currents. 
Whenever  the  character  of  the  surface  (as,  for  in- 
stance, that  of  the  great  lakes  or  the  ocean)  is  such 
as  to  reduce  the  friction  to  the  minimum,  these  follow- 
ing winds  will  blow  with  much  greater  velocity  near 
the  earth's  surface  than  they  do  over  the  broken  lands. 
Instances  verifying  this  opinion  are  apparent  on  any 
weather  map  of  the  United  States  where  the  low  area 
has  been  sharply  followed  by  the  descending  high  area. 
It  is  probable  that  the  abnormally  high  winds  of  San- 
dusky,  O.,  Cape  Hatteras,  N.  C.,  and  other  exposed 
points  along  the  lakes  and  seaboard  can  be  explained 
by  the  sudden  diminution  in  the  amount  of  friction 
experienced  by  the  surface  winds. 

To  summarize,  low-area  storms  have  a  wind  circula- 
tion inward  and  upward,  are  elliptical  in  form,  in  the 
United  States,  generally,  have  their  major  axis  from 
W.  S.  W.  to  E.  N.  E.,  have  a  mean  velocity  varying 
from  600  to  900  miles  each  day,*  move  in  the  same  gen- 
eral direction,  probably,  as  the  upper  air  currents, 
usually  toward  a  point  varying  a  little  from  due  east, 
are  characterized  in  their  eastern  quadrants  by  cloudy 
weather,  southerly  and  easterly  winds,  precipitation, 
temperature  oppressive  in  summer  and  abnormally  high 
in  winter,  falling  barometer,  increasing  humidity  ;  and 
followed  by  clearing  weather,  rising  barometer,  de- 
creasing humidity,  and  falling  temperature  in  the  west- 
ern quadrants.  These  latter  changes  are  more  decided 
in  the  United  States  than  in  Europe,  since  in  this 
country  the  air  drawn  in  behind  the  depression  is  a 
cold,  dry  current  from  the  comparatively  high  press- 


*  The  cyclones  of  the  "West  Indies  travel  with  only  about  one  half  of 
this  velocity.  It  is  to  be  noted  that  the  progressive  movement  of  storms 
is  less  rapid  over  ocean  than  across  land, 


192  AMERICAN   WEATHER. 

ure  of  sub-arctic  America,  while  Europe  receives  some- 
what humid  and  cool  winds,  whose  force  fails  to  attain 
the  maximum,  on  account  of  the  permanent  low  press- 
ures to  the  northwest  in  the  vicinity  of  Iceland. 
When  the  pressure  to  the  northwest  of  Great  Britain 
is  abnormally  high,  from  April  to  June,  the  conditions 
in  the  wake  of  storms  are  almost  as  persistent  and 
marked  as  in  the  United  States,  the  northwest  winds 
being  stronger,  colder,  and  dryer  than  at  other  sea- 
sons. 


CHAPTER  XIY. 

CYCLONES  AND  HURRICANES. 

THE  difference  between  an  ordinary  storm  and  a 
cyclone  consists  largely  in  the  path  of  the  storm's 
movement,  although  some  other  characteristics  dis- 
tinguish it  from  an  ordinary  low-area  storm,  as  has 
been  set  forth  in  a  preceding  chapter. 

The  cylcone  of  August  16th  to  22d,  1888,  has  been 
selected  as  a  storm  representative  of  both  the  hurri- 
canes from  the  West  Indies  and  an  ordinary  low-area 
storm  of  the  United  States.  It  will  be  noticed  from  the 
track  on  Fig.  30  that  this  storm  travelled  in  the  usual 
parabolic  path,  that  its  change  of  curvature  from  the 
northwest  to  the  northeast  took  place  in  about  latitude 
30°  K,  that  its  velocity  from  the  Gulf  of  Mexico  was 
considerably  lower  than  over  the  land,  and  that  this 
velocity,  which  was  slowest  near  the  apex  of  the  para- 
bola, increased  to  a  marked  extent  after  the  change 
in  its  direction  of  motion  to  the  northeast  had  taken 
place. 

The  weather  conditions  at  8  A.M.,  August  21st,  are 
shown  in  Fig.  30  by  conventional  signs.  Clear  weather 
prevails  over  the  unshaded  part  of  the  map  and  rainy 
weather  over  the  deeply  shaded  part,  while  the  inter- 
mediate tint  represents  the  districts  covered  with 
clouds.  The  small  figures  near  each  station  show  the 
amount  of  rain  which  has  fallen  in  twelve  hours  previ- 
ous to  the  time  of  the  map.  The  arrows  fly  with  the 
wind,  and  by  the  number  of  fieches,  or  barbs,  indicate 


-, 


194 


AMERICAN   WEATHER. 


its  strength.     S&Kfteches  would  represent  the  strongest 
winds  known,  and  one  denotes  light  airs.     The  dotted 


FIG.  30. 


path  shows  the  entire  track  of  the  centre  of  the  cy- 
clone, and  the  circles  designate  its  position  at  8  A.M. 
and  8  P.M.,  respectively,  on  the  dates  placed  over  them. 


AMERICAN   WEATHER.  195 

The  storm  was  first  indicated,  August  16th,  1888,  by 
very  heavy  precipitation,  2.20  inches  in  twelve  hours, 
at  Point  Jupiter,  Fla.,  with  an  easterly  wind  of  sixty 
miles  per  hour.  Its  passage  westward  over  the  Gulf  of 
Mexico  during  the  17th  was  very  slow,  and  it  was  not 
until  the  morning  of  August  20th  that  it  curved  to 
north  and  passed  into  the  land  regions  of  the  United 
States,  in  Western  Louisiana.  Its  most  marked  vio- 
lence over  land  regions  did  not  occur  until  the  night  of 
the  19th-20th,  when  its  passage  northeast  to  Ten- 
nessee was  marked  by  violent  southerly  winds  of  fifty- 
five  miles  at  Mobile,  La.,  and  sixty  miles  at  Pensacola, 
Fla.,  together  with  heavy  precipitation.  At  the  same 
time,  the  rainfall  at  Vicksburg,  Miss.,  amounted  to 
nearly  three  inches  in  twenty-four  hours,  while  that  at 
Memphis,  Tenn.,  near  the  path  of  the  cyclone,  was 
3.74  inches  in  twelve  hours.  By  8  A.M.  of  August  21st 
it  had  moved  into  Central  Kentucky,  where  the  ba- 
rometer stood,  at  Louisville,  29.46  inches,  with  about 
two  inches  of  rainfall  over  all  of  Kentucky  and  Cen- 
tral Tennessee. 

The  peculiar  characteristics  of  a  low-area  storm 
were  everywhere  evident,  and  in  observing  this  storm, 
as  shown  in  Fig.  30,  the  pertinence  of  Buys  Bal- 
lot's law  of  winds  is  at  once  evident.  This  law  is 
that  in  the  Northern  Hemisphere,  if  one  stands  with 
back  to  the  wind,  the  lowest  barometric  pressure  will 
be  invariably  to  the  left  hand.  In  the  Southern 
Hemisphere  the  lowest  pressure  is  always  to  the 
right.  It  will  be  observed  that  the  eighteen  circumja- 
cent stations  in  Kentucky,  Tennessee,  and  from  Il- 
linois eastward  to  Indiana  have  winds  which  are  en- 
tirely in  accord  with  this  law,  and  that  these  winds 
are  blowing  inward  toward  the  centre,  crossing  the 
isobars  at  angles  varying  from  fifty  to  eighty  de- 


196  AMEKICAN   WEATHEE. 

grees.  This  inclination  is  somewhat  ]ess  than  in  the 
case  of  the  Indian  cyclones,  where  Blanford  says  that 
in  the  northeast  and  northwest  quadrants  one  must 
face  the  wind  exactly  and  the  direction  of  the  storm 
centre  will  be  eleven  points  (about  one  hundred  and 
twenty-five  degrees  azimuth)  to  the  right.  This  rule, 
he  adds,  is  not  so  exactly  applicable  in  the  southern 
quadrants. 

In  the  easterly  quadrants  are  seen  cloudy  weather 
and  rain,  with  easterly  winds  and  high  temperature, 
and  in  the  western  quadrants  winds  from  north  to 
west,  lower  temperature,  and  clearing  weather.  At 
this  period  of  the  storm's  history  it  might  be  in- 
ferred that  its  subsequent  direction  would  be  to  the 
northeast,  so  as  to  cross  Lake  Ontario  and  pass 
down  the  valley  of  the  St.  Lawrence — a  course  fol- 
lowed by  so  many  low-area  storms  of  the  United 
States.  It  is  possible,  as  has  been  suggested  by 
Lieutenant  Dunwoody,  that  the  later  slightly  ab- 
normal movement  of  the  storm  to  the  east-north- 
east, instead  of  to  the  northeast,  might  have  been  pred- 
icated from  the  peculiar  path  before  the  recurvature  ; 
since  in  many  cases  it  happens  that  the  angle  of 
inclination  toward  the  northwest  in  the  west  path 
before  such  recurvature  is  substantially  the  same  as 
that  followed  to  the  northeast  after  recurvating.  How- 
ever this  may  be,  there  were  good  reasons  for  predict- 
ing that  the  storm  would  pass  to  the  east-northeast, 
the  most  obvious  of  which  has  been  dwelt  upon  in  the 
preceding  chapter — that  is,  heavy  rainfall  in  front  of 
the  storm.  It  will  be  noticed  that  in  the  previous 
twelve  hours  to  8  A.M.  of  August  20th— the  time  of  the 
storm  shown  in  Fig.  30 — no  rain  had  fallen  at  any  sta- 
tion on  Lake  Erie  or  Lake  Ontario,  but  that  the  heavy 
rainfall  of  an  inch  and  a  half  had  occurred  at  Harris- 


AMERICAN    WEATHER.  197 

burg,  Pa.,  in  the  twelve  hours,  while  more  or  less  pre- 
cipitation had  occurred  at  other  places  in  Pennsylvania, 
Maryland,  and  Virginia.  It  was  doubtless  the  influence 
of  this  precipitation  and  of  the  cloud  formation  accom- 
panying it  which  determined  the  more  easterly  path  of 
the  cyclone. 

Nearly  three  inches  of  rain  fell  within  the  twelve 
hours  following  over  Southern  Pennsylvania,  New 
Jersey,  and  the  vicinity  of  New  York,  in  the  direct 
path  over  which  the  cyclone  later  passed,  and  its  sub- 
sequent passage  to  the  east-northeast  through  Connec- 
ticut was  marked  by  rainfalls  between  three  and  four 
inches  in  twelve  hours,  in  advance  of  tlie  centre. 

The  passage  of  this  storm  resulted,  as  do  all  the  hur- 
ricanes of  the  West  Indies  which  pass  over  any  land 
region,  in  immense  damage  to  crops,  buildings,  bridges, 
and  everything  which  could  be  injured  by  excessive 
rains,  severe  local  floods,  or  violent  winds.  In  Louisi- 
ana alone  the  damage  was  estimated  at  about  one  half 
million  dollars,  and  it  is  probable  that  the  damage  for 
the  whole  country  could  be  hardly  less  than  a  million 
dollars. 

This  storm,  however,  was  not  one  of  the  most  violent 
of  those  from  the  Caribbean  Sea,  of  which  the  fol- 
lowing are  mentioned  as  the  most  remarkable  and 
destructive  of  late  years. 

The  hurricane  which  devastated  Guadaloupe,  Septem- 
ber 6th,  1865,  is  notable  not  only  for  its  destruction  of 
property  and  life  on  that  island,  but  also  owing  to  the 
very  remarkable  decrease  of  pressure,  1.693  inches  in 
seventy  minutes— from  29.646  at  6.30  A.M.  to  27.953  at 
7.40  A.M. — which  occurred  during  its  passage. 

The  hurricane  of  August  14th-27th,  1873,  known  as 
the  Nova  Scotia  cyclone,  was  the  most  destructive  storm 
which  has  ever  visited  the  Atlantic  coast,  It  recurved 


198  AMERICAN   WEATHER. 

between  the  island  of  Bermuda  and  Cape  Hatteras, 
N.  C.,  and  its  centre  at  no  time  touched  the  coast  line. 
Its  ravages  were  such  that  the  storm  has  well  been 
termed  terrible.  Twelve  hundred  and  twenty-three 
vessels  were  known  to  have  been  destroyed  by  it,  and 
223  human  lives  were  definitely  reported  as  lost.*  It 
was  estimated  that,  including  crews  of  missing  vessels 
and  lives  lost  on  land,  at  least  six  hundred  persons 
perished  from  this  hurricane. 

The  storm  seriously  crippled  the  fishing  industries 
of  both  Canada  and  the  United  States,  and  besides 
bringing  sorrow  and  death  to  hundreds  of  homes,  en- 
tailed a  pecuniary  loss  estimated  at  over  three  and  one 
half  millions  of  dollars. 

A  cyclone  secondary  to  this  in  violence,  but  also 
marked  by  a  fearful  loss  of  human  life,  is  that  of  Sep- 
tember 15th,  1875,  which,  recurving  at  Indianola,  Tex., 
and  nearly  destroying  that  town,  moved  northeastward 
across  the  United  States,  and  left  the  coast  between 
capes  Henry  and  May.  There  were  serious  marine 
disasters  on  the  New  Jersey  coast,  but  these  sank  into 
insignificance  compared  with  the  fate  of  Indianola. 
Hurricane  winds  of  eighty-eight  miles  per  hour  were 
recorded  at  that  place,  which,  with  a  general  inunda- 
tion from  the  sea,  proved  fatally  disastrous.  One 
hundred  and  seventy-six  lives  were  lost  and  three 
fourths  of  the  town  was  swept  away,  entailing  a  loss 
of  over  a  million  dollars'  worth  of  property. 

In  September,  1877,  a  hurricane  on  the  21st  passed 
near  to  Barbadoes  and  on  the  23d  swept  over  Buen 
Ayre  and  Curagoa.  On  the  latter  island  shipping  was 
much  damaged,  solid  buildings  in  the  city  of  Curagoa 


*  A  full  account  of  this  storm,  prepared  by  Professor  C.  Abbe,  is  to  be 
found  in  the  report  of  the  Chief  Signal  Officer,  1873. 


AMERICAN   WEATHER.  199 

swept  away,  many  lives  lost,  and  a  damage  over  two 
millions  of  dollars  done  to  property.  After  recurving, 
it  moved  across  Florida  near  St.  Mark's,  and  passing 
over  Chesapeake  Bay  left  the  Atlantic  coast  near  Cape 
Cod.  Its  passage  through  the  Atlantic  States,  marked 
by  violent  winds  and  excessive  rains,  did  great  damage 
to  cotton  and  rice  crops,  bridges,  railroads,  etc.,  and 
shipwrecked  several  steamers  and  other  vessels. 

Hurricane,  October  21s£-24^,  1878.  It  first  dam- 
aged buildings  and  sank  vessels  at  Havana.  It  entered 
the  United  States  near  Wilmington,  N.  C.,  and  mov- 
ing due  north,  passed  over  Washington  and  Eastern 
Pennsylvania,  after  which  it  curved  eastward,  and, 
crossing  New  England,  left  the  coast  near  Portland,  Me. 
In  Philadelphia  over  seven  hundred  substantial  build- 
ings were  totally  destroyed  or  seriously  damaged, 
bridges  injured,  twenty-two  vessels  sunk,  several  per- 
sons injured,  and  eight  perished,  entailing  a  loss  vari- 
ously estimated  from  one  to  two  millions  of  dollars. 
Other  loss  of  life  and  great  damage  by  freshets  and 
winds  occurred  elsewhere  in  Pennsylvania.  A  large 
number  of  steamers,  ships,  and  coasting  vessels  were 
dismantled,  wrecked,  or  sunk  along  the  New  Jersey, 
Virginia,  and  North  Carolina  coasts,  entailing  loss  of 
life  and  enormous  pecuniary  damage.  The  -  wind 
reached  seventy-two  miles  per  hour  at  Philadelphia, 
and  from  eighty  to  eighty-eight  miles  along  the  coast. 

Hurricane,  August  I6t7i-2Qth,  1879.  Entered  the 
United  States  at  Cape  Lookout,  N.  C.,  and  skirted  the 
Atlantic  coast,  thence  northeastward  to  Eastport,  Me. 
An  enormous  amount  of  damage  resulted  from  this 
storm.  Not  only  was  the  injury  to  inland  property 
very  excessive,  but  the  damage  to  maritime  interests 
may  be  estimated  from  the  fact  that  over  one  hundred 
large  vessels  were  shipwrecked,  dismantled,  or  dis- 


200  AMERICAN  WEATHER. 

abled,  and  two  hundred  yachts  or  smaller  vessels  in- 
jured. The  wind  reached  a  measured  velocity  of  138 
miles  per  hour  at  Cape  Lookout,  where  the  anemometer 
was  carried  away.  The  barometer  fluctuated  with  ex- 
traordinary rapidity,  there  being  off  the  New  Jersey 
coast  a  fall  of  0.85  inch  in  five  and  one  half  hours,  fol- 
lowed by  a  rise  of  0.93  in  six  and  one  half  hours. 

Jamaica  hurricane,  August  17tk,  18th,  1880.  Dev- 
astated nearly  all  Jamaica,  at  least  twelve  lives  be- 
ing lost  and  hundreds  of  buildings  destroyed. 

August  23d-28th,  1881.  Entered  the  United  States 
near  Savannah  and  followed  a  very  unusual  course  to 
the  northwestward  to  Minnesota.  The  loss  of  life  and 
damage  to  property  in  Charleston,  S.  C.,  Tybee  Island, 
and  along  the  adjacent  coast  w^ere  very  great.  About 
four  hundred  persons  lost  their  lives,  and  hundreds  of 
houses  were  totally  destroyed.  The  loss  of  property  is 
estimated  at  over  one  and  one  half  millions  of  dollars. 
A  similar  storm  passed  over  Charleston  August  23d, 
24th,  1885,  where  damage  to  the  extent  of  nearly  two 
millions  of  dollars  was  done,  and  twenty-one  lives 
were  lost. 

At  Manzanilla,  October  27th,  1881,  a  hurricane 
wrecked  all  vessels  but  one,  and  destroyed  nearly  every 
house,  entailing  a  loss  of  $500,000. 

A  hurricane,  October  8th-14th,  1882,  crossed  Cuba, 
causing  great  loss  of  life  and  enormous  destruction  to 
property.  Thousands  of  houses  were  completely  de- 
molished and  others  seriously  damaged.  About  forty 
persons  were  killed  and  thousands  of  cattle  drowned. 
Its  passage  along  the  Atlantic  coast  was  marked  by 
violent  gales  and  great  loss  of  shipping,  but  urgent 
and  timely  storm  warnings  detained  most  vessels  in 
port  until  the  hurricane  passed.  Fifteen  steamers  and 
over  two  hundred  sailing  vessels,  covering  property  es- 


AMERICAN  WEATHER.  201 

timated  to  be  from  eight  to  ten  millions  of  dollars  in 
value,  were  detained  at  New  York  by  timely  notice  of 
the  violent  storm.  On  the  Labrador  coast  over  seven- 
ty vessels  were  lost,  and  probably  100  men  perished. 

August  19th,  20th,  1886,  a  cyclone  completely  de- 
stroyed Indianola,  Tex.,  which,  as  before  stated,  was 
nearly  swept  away  in  September,  1875.  Not  a  house 
was  left  standing,  and  over  twenty  lives  were  lost. 
Galveston,  Tex.,  also  suffered  great  damage. 

It  must  not  be  supposed  that  even  the  worst  of  the 
cyclones  of  North  America  stand  unequalled  in  vio- 
lence, destruction,  and  death-list.  The  violent  cyclones 
of  the  Indian  Ocean  and  the  China  Sea  have  been  at 
times  so  destructive,  not  of  property  alone,  but  of 
human  lives,  that  the  mind  of  any  reflecting  man 
is  appalled  at  the  record  of  misery  and  death  wrought 
by  these  terrible  outbursts  of  nature's  forces. 

The  great  difference  between  the  pressure  at  the  storm 
centre  and  its  rear  sometimes  causes  a  storm  wave  to 
follow  in  the  path  of  the  cyclone,  thus  overwhelming 
such  low-lying  level  lands  as  are  in  its  course.  In 
such  cases,  if  the  land  is  inhabited,  the  loss  of  life  is 
occasionally  enormous. 

The  Calcutta  cyclone  of  October  5th,  1864,  followed 
by  a  storm  wave  of  sixteen  feet  over  the  level  delta  of 
the  Ganges,  caused  the  death  of  45,000  persons. 

The  Backergunge  cyclone  of  October  31st,  1876,  was 
accompanied  by  an  unparalleled  storm  wave,  which 
covered  the  eastern  edge  of  the  delta  of  the  Ganges 
with  water  from  ten  to  nearly  fifty  feet  deep.  Accord- 
ing to  the  lowest  estimate,  over  one  hundred  thousand 
persons  perished  from  this  wave. 


CHAPTER  XV. 

AEEAS   OF   HIGH  PRESSURE. 

As  may  be  inferred  in  the  treatment  of  low  areas, 
they  are  nearly  always  of  sufficient  intensity  to  merit 
the  name  of  storms,  but  such  term  can  be  applied  less 
frequently  to  the  other  systems  of  pressure,  known  as 
high  areas,  in  which  the  barometric  pressures  are  de- 
fined by  isobars  successively  higher  toward  the  centre. 

The  high  areas  are  quite  frequently  called  anti- 
cyclones, since  the  general  direction  of  the  winds  con- 
nected with  high-area  storms  is  almost  diametrically 
opposite  to  that  of  the  low-area  winds.  Buys  Ballot's 
law  applies  to  anti-cyclones  as  well  as  to  cyclones— 
that  is,  when  one's  back  is  to  the  wind  the  barometer 
is  lowest  in  the  Northern  Hemisphere  to  the  left  hand 
and  liigliest  to  the  right  hand.  It  thus  follows  that 
in  the  cyclone,  as  has  been  set  forth,  the  winds  blow 
inward,  in  a  direction  contrary  to  the  motion  of  the 
hands  of  a  watch  in  the  Northern  Hemisphere,  and  the 
winds  of  a  high  area,  or  anti-cylcone,  blow  outward, 
in  a  direction  agreeing  with  the  motion  of  the  hands 
of  a  watch.  The  angle  at  which  the  winds  blow  out- 
ward in  anti-cyclones  is  somewhat  slighter  than  the 
inclination  of  winds  inward  toward  the  centre  of  a  low 
area. 

The  isobars  enclosing  high  areas  are  somewhat  more 
regular  than  those  of  low  areas,  but  rarely  assume 
either  a  circular  or  pronounced  elliptical  form.  Pro- 
fessor Russell  has  invited  the  author's  attention  to  the 


AMEBICAK  WEATHER.  203 

recurrence  of  anti-cyclones  with  triangular-shaped  iso- 
bars. Many  such  cases  appear  on  the  United  States 
weather  maps,  of  which  a  typical  one  is  that  of  Jan- 
uary 13th,  1885. 

In  the  United  States  anti-cyclones  are  about  forty 
per  centum  less  frequent  than  low-area  storms. 

The  number  of  high  areas  increases  slowly  from  five 
in  June  to  eight  in  January,  February,  and  March,  and 
then  decreases  regularly  to  June  again.  It  is  more 
than  probable  that  the  velocity  of  the  movement 
changes  correspondingly,  as  in  the  case  of  low  areas, 
with  the  varying  frequency — that  is,  the  average  veloc- 
ity is  lower  in  the  summer  months,  when  such  storms 
are  infrequent,  and  is  at  its  maximum  during  the 
winter  months,  when  the  greatest  number  of  cyclones 
or  anti-cyclonic  areas  occur.  Owing  to  the  less  rela- 
tive importance  of  anti-cyclones,  their  progressive 
movement  has  not  been  determined  as  frequently  or 
satisfactorily  as  the  movement  of  cyclones.  In  all 
cases  where  such  velocity  has  been  determined,  it  ap- 
pears that  high  areas  do  not  move  with  the  same  aver- 
age velocity  as  do  the  low  areas,  the  difference  amount- 
ing to  ten  or  fifteen  per  centum. 

Probably  not  more  than  one  third  of  the  entire  anti- 
cyclonic  areas  can  be  classed  as  storms,  if  that  term  is 
closely  restricted  to  atmospheric  disturbances  of  such 
extent  as  to  materially  modify  the  course  and  at  the 
same  time  augment  the  velocity  of  the  surface  winds. 
Indeed,  most  of  the  anti-cyclones  in  summer  are  at- 
tended by  light  or  fresh  winds  of  sufficiently  low  tem- 
perature to  agreeably  modify  the  excessive  summer 
heats  of  the  United  States.  In  winter  the  advance  of 
these  high  areas,  though  always  attended  by  a  decided 
fall  in  temperature,  is  for  the  most  part  characterized 
by  calms  near  the  centre  and  light  or  fresh  winds  on 


204  AMERICAN  WEATHER. 

the  outskirts  of  the  area,  the  winds  not  rising  to  a 
sufficient  strength  to  be  either  important  or  dangerous. 

Although  the  advancing  edge  of  an  anti- cyclone, 
especially  when  following  closely  in  the  wake  of  a  pass- 
ing low  area,  is  often  accompanied  by  high  winds  and 
precipitation,  in  the  form  of  snow  or  rain,  yet  such  is 
not  the  predominating  characteristic  of  these  areas. 
As  a  general  rule,  the  anti-cyclone  is  marked  by  clear 
skies,  abnormally  low  temperature,  and  calms  or  light 
winds.  Near  the  centre  of  the  area  especially  there 
are  neither  surface  winds  nor  clouded  skies.  This 
clear,  calm  condition  of  the  atmosphere  at  the  surface 
of  the  earth  permits  rapid  nocturnal  radiation,  while  at 
the  same  time  the  air  strata  near  the  earth  gain  no  heat 
by  convection. 

This  condition  of  affairs  tends  to  lower  the  tempera- 
ture of  the  air  at  the  centre  of  an  anti- cyclone,  if,  in- 
deed, this  process  of  nocturnal  radiation  through  a 
very  dry  atmosphere  is  not  the  important  factor  in  in- 
ducing and  continuing  the  abnormally  low  tempera- 
ture. In  connection  with  this  point,  it  is  interesting  to 
note  that  far  the  greater  part  of  the  anti-cyclones  of 
the  United  States  come  from  Manitoba  or  Saskatche- 
wan, yet  the  lowest  temperature  noted  in  such  areas 
obtains  not  in  the  northern  parts  of  these  districts,  but 
very  near  the  49th  parallel,  the  boundary-line  between 
the  United  States  and  British  America.  It  seems  prob- 
able that  in  its  passage  southward  the  air  becomes 
gradually  colder,  owing  to  the  favorable  conditions  of 
the  high  treeless  plateaus  for  nocturnal  radiation,  but 
finally  a  point  is  necessarily  reached  in  the  southward 
course  where  the  days  are  longer,  and  the  heat  received 
from  the  sun  must  more  than  counterbalance  that  lost 
by  nocturnal  radiation.  The  absence,  too,  of  aqueous 
vapor  tends  to  increase  the  density  of  the  air,  and  pos- 


AMERICAN  WEATHER.  205 

sibly  these  two  conditions,  creating  dryness  and  very 
low  temperatures,  are  sufficient  to  cause  the  increased 
density  of  the  lower  strata  of  the  air  to  such  an  extent 
as  to  form  an  anti-cyclone. 

It  is  believed  that  far  the  larger  number  of  anti- 
cyclones which  pass  eastward  over  the  United  States 
are  of  limited  depth,  as  shown  by  conditions  on  the 
summit  of  Mount  Washington  (6279  feet).  It  has  been 
noticed  frequently  by  the  author  that  a  large  number 
of  anti-cyclonic  areas  depend  for  direction  and  mo- 
tion upon  phenomena  occurring  in  strata  of  air  of 
very  moderate  thickness,  since  the  Alleghanies,  the 
Blue  Ridge  and  at  times  even  the  low  mountains  in 
Arkansas  are  sufficient  to  break  up,  divert,  or  materi- 
ally modify  the  course  and  action  of  such  areas. 

In  connection  with  anti-cyclones  there  prevail,  how- 
ever, from  time  to  time,  especially  in  the  winter 
months,  severe  storms  of  wind,  either  with  or  without 
snow.  When  accompanied  by  snow  they  are  popularly 
known  in  the  northwestern  part  of  the  United  States 
as  "  blizzards."  These  will  be  treated  of  in  a  subse- 
quent chapter,  in  connection  with  the  sudden,  severe, 
and  widely-extended  changes  of  temperature  known 
as  cold  waves. 

Apart  from  these  storms,  which  occur  through  the 
rapid  advance  of  an  anti-cyclone  in  the  wake  of  a 
cyclone,  may  be  mentioned  other  storms  which  result 
from  the  natural  operations  of  the  anti-cyclone  itself, 
independent  of  any  well-defined  adjacent  cyclone. 

It  was  remarked  first  by  Franklin,  I  believe,  that 
the  phenomena  in  the  United  States  known  as  north- 
east storms,  while  attended  by  northeast  winds,  really 
came  from  the  southwest,  and  that  such  storms  prevail 
first  in  Pennsylvania,  later  in  Connecticut,  and  still 
later  in  Maine.  While  this  is  true  as  a  general  rule, 


206  AMEKICAN   WEATHER. 

yet  there  are  marked  exceptions.  Franklin' s  observa- 
tions and  theory  were  sound  as  far  as  they  went,  but 
it  has  been  shown  by  the  experience  of  so  remarkable 
and  skilled  a  meteorologist  as  Dove  that  special  me- 
teorological phenomena  pertain  to  limited  sections  of 
the  earth's  surface,  and  that  any  deduction  from  local 
atmospheric  changes  cannot  be  rigidly  applied  in  a  gen- 
eral manner.  Dove's  opinion  on  the  march  of  weather 
phenomena  in  connection  with  the  passage  of  low-area 
storms  over  Europe  was  based  on  observations  cover- 
ing France  and  Germany — countries  which,  as  a  rule, 
lie  to  the  southward  of  the  storm  tracks — and  his  state- 
ment left  unconsidered  the  march  of  such  phenomena 
on  the  north  side  of  the  storm  tracks,  such  as  obtains 
so  frequently  in  Scotland  and  Iceland. 

In  like  manner,  the  northeast  storms  which  prevail 
in  connection  with  anti-cyclones  are  infrequent,  and 
so  have  not  received  the  attention  they  deserve.  Their 
very  infrequency  and  suddenness  make  them,  how- 
ever, dangerous,  since  they  come,  as  it  were,  as  a  thun- 
derbolt from  a  clear  sky,  the  storm  frequently  begin- 
ning first  along  the  Southern  New  England  coast  as  a 
northerly  one  and  extending  southward  to  the  New 
Jersey  and  North  Carolina  coasts,  in  which  latter 
places  they  change  to  northeasterly  and  blow  with 
exceeding  violence. 

A  typical  case  of  such  northeasterly  gales  is  that  in 
connection  with  the  anti-cyclone  of  October  13th-16th, 
1884.  Its  centre  was  over  North  Minnesota,  October 
13th,  from  which  section  it  moved  eastward  across  the 
great  lakes,  and  was  to  the  northward  of  Lakes  Erie 
and  Ontario  on  October  15th.  In  connection  with  this 
area,  the  winds  during  the  14th  blew  from  the  north  and 
northwest  in  New  England,  while  on  the  New  Jersey 
and  North  Carolina  coasts  they  were  from  the  north- 


AMERICAN   WEATHER. 


207 


east,  fortunately  with  a  clear  sky.  For  over  twenty- 
four  hours  the  wind  along  the  New  Jersey  coast  blew 
with  a  velocity  ranging  from  twenty -five  to  the  un- 
usual velocity  of  fifty-two  miles  per  hour,  and  along 
the  North  Carolina  coast  from  twenty-five  to  forty- 
seven  miles  per  hour.  Along  all  these  coasts  north- 
easterly gales  were  experienced,  causing  more  or  less 
damage  to  shipping.  There  was  no  connection  with 
any  other  adjacent  storm  centre,  and  the  winds  were 
purely  anti-cyclonic.  It  may  further  be  advanced  that 
these  winds  were  higher  than  the  barometric  gradient 
appeared  to  justify,  and  it  is  probable  that  their  force 
largely  depended  on  a  temperature  gradient. 


Chart  shming f Anti-Cyclone  at  8ajtJ.  JaxL,12*  1886. 


FIG.  81. 


The  conditions  represented  on  Fig.  31  are  character- 
istic of  anti-cyclonic  storms.  The  centre  in  Southern 
Missouri  and  Northern  Arkansas  is  marked  by  calms 
or  light  winds.  The  weather  over  the  entire  country 
is  clear,  there  being  no  clouds  except  at  a  few  coast 


208  AMERICAN  WEATHER. 

and  lake  stations,  and  precipitation  in  the  previous 
eight  hours  has  occurred  only  on  the  Texas  coast,  in 
the  form  of  light  snow. 

This  anti-cyclone  followed  the  path  peculiar  to  many 
— that  is,  from  Dakota  southward  to  the  vicinity  of 
the  Gulf  coast,  whence  high  areas  drift  eastward  with 
the  general  atmospheric  circulation.  During  the  prev- 
alence of  such  areas  the  cold  period  is  prolonged,  rarely 
being  less  than  five,  and  frequently  as  much  as  seven 
days  in  duration. 

Another  path  much  frequented  by  anti-cyclones  is 
from  Manitoba  eastward  to  the  Gulf  of  St.  Lawrence. 
In  such  cases  the  northern  part  of  the  country  only  is 
affected  by  the  fall  of  temperature,  which  is  sharp 
and  of  brief  duration,  rarely  exceeding  three  days. 
Such  high  areas,  as  has  been  mentioned,  from  their 
peculiar  wind  circulation  are  liable  to  produce  north- 
east gales  along  the  New  England  and  Middle  Atlantic 
coasts. 

The  most  generally  destructive  anti-cyclone  that  has 
appeared  over  the  United  States  for  many  years  is 
doubtless  that  of  January  5th-14th,  1886,  when  the 
damage  by  low  temperatures  amounted  to  several  mill- 
ions of  dollars.  The  outskirts  of  this  anti-cyclone  ap- 
peared January  6th,  in  rear  of  a  low-area  storm  of  great 
severity,  which  developing  over  the  western  part  of 
the  Gulf  of  Mexico,  moved  eastward  to  Georgia,  and 
thence  northeastward  over  New  England.  A  steady 
outflow  of  cold  air  from  British  America  continued  for 
several  days,  during  which  time  it  appears  probable 
that  the  centre  of  the  high  area  moved  in  a  direction  a 
little  east  of  south  from  the  Pease  River  country  to 
Eastern  Dakota,  where  it  was  central  on  the  llth.  At 
this  time  the  temperature  was  more  than  thirty  de- 
grees below  zero  in  British  America,  while  zero  tern- 


AMERICAN  WEATHER.  209 

peratures  covered  the  entire  Missouri  Valley  and  the 
Mississippi  Valley  southward  nearly  to  Vicksburg. 
The  progress  in  the  next  twenty-four  hours  was  rapid, 
and  on  the  morning  of  January  12th  its  centre  was  in 
Southeastern  Missouri.  From  Missouri  the  area  drifted 
eastward,  and  slowly  passed  off  the  Atlantic  coast  on 
the  14th. 

The  atmospheric  conditions  at  7  A.M  of  the  12th  are 
shown  on  Fig.  31,  on  which  chart  is  shown  the  track 
of  the  anti-cyclone  from  British  America  to  the  At- 
lantic seaboard.  At  that  time  the  entire  country  to 
the  eastward  of  the  Rocky  Mountains  was  affected  by 
temperatures  ranging  from  thirty  degrees  below  zero 
over  Canada  to  thirty  degrees  above  zero  at  Browns- 
ville, Tex.  There  was  no  portion  of  Florida  from 
which  reports  were  received  but  what  experienced 
freezing  temperatures  and  hard  frosts,  and  only  the 
extreme  southeastern  part  of  the  State  escaped  injury. 
At  Key  West  the  temperature  fell  to  forty-two  de- 
grees, the  lowest  ever  recorded. 

Galveston  Bay  froze  over  on  the  9th,  and  snow  fell 
through  all  of  Southern  Texas,  from  San  Antonio 
southward  to  Brownsville,  it  being  the  first  general 
snow  in  that  region  since  1866.  At  Pensacola,  FlaM 
fresh- water  ice  formed  to  the  thickness  of  three  inches, 
and  sea  water  froze  along  the  edge  of  the  bay.  In 
Florida,  at  Manatee,  Live  Oak,  Lake  City,  Cedar 
Keys,  and  Tampa,  ice  of  considerable  thickness  formed. 
In  Florida  alone  the  damage  to  fruit  and  to  other  in- 
terests was  estimated  at  over  two  millions  of  dollars. 

The  anti-cyclone  of  January,  1886,  was  the  most 
noteworthy  one  for  many  years,  as  it  induced  in  the 
Gulf  States  the  lowest  temperatures  ever  recorded, 
although  a  similar  storm  of  about  the  same  severity 
occurred  in  1835. 


210  AMERICAN   WEATHEE. 

A  storm  of  a  similar  character  occurred  December 
27th-31st,  1880,  when  the  high-area  central  over  Mani- 
toba, on  the  morning  of  the  27th,  moved  due  southward, 
and  reached  Central  Texas  on  the  morning  of  the  30th, 
whence  it  gradually  moved  eastward  and  dissipated. 
This  anti-cyclone  also  followed  low- area  storms  which 
passed  from  Texas  to  Georgia.  This  high  area  was 
nearly  as  severe  as  the  one  of  January,  1886,  as  far  as 
the  Gulf  States  were  concerned,  and  during  it  the  low- 
est temperature  for  fifty  years  also  occurred  in  many 
parts  of  Pennsylvania,  Maryland,  Virginia,  and  North 
Carolina. 

During  the  anti-cyclone  of  December,  1880,  the  tem- 
perature fell  at  Fort  Benton  to  fifty-nine  degrees  be- 
low zero,  and  on  the  morning  of  December  30th,  31st, 
freezing  temperatures  prevailed  over  the  entire  United 
States,  except  in  the  Pacific  coast  region,  the  southern 
half  of  Florida,  and  the  extreme  southwestern  portion 
of  Arizona. 

As  forming  special  and  important  classes  of  anti- 
cylones,  cold  waves  and  blizzards  are  considered  suf- 
ficiently national  and  American  to  warrant  their  sep- 
arate description  in  some  detail. 


CHAPTER  XVI. 

COLD   WAVES   AND  BLIZZARDS. 

THE  term  "  cold  wave"  is  a  technical  one  devised 
by  the  United  States  Signal  Service,  not  to  represent 
the  intensity  of  the  cold,  except  within  certain  limits, 
but  more  especially  to  show  very  decided  falls  in  tem- 
perature within  a  limited  time.  The  cold  wave  of  the 
Signal  Service  indicates  (1)  that  the  minimum  tem- 
perature will  sink  to  forty-five  degrees  Fahrenheit  or 
below,  and  (2)  that  a  fall  of  fifteen  degrees  or  more 
will  take  place  from  any  given  hour  of  one  day  (as 
8  A.M.  or  P.M.)  until  the  same  hour  of  the  next 
day.  As  has  been  shown  in  treating  of  ranges,  it  is 
no  unusual  thing  at  elevated  stations  in  Arizona  for 
the  temperature  to  fall  fifty  degrees  from  the  maxi- 
mum of  one  afternoon  to  the  minimum  of  the  next 
morning,  a  period  of  twelve  or  fourteen  hours  ;  but 
in  most  of  these  cases  the  fall  from  the  maximum  or 
minimum  of  one  day  to  the  maximum  or  minimum  of 
the  succeeding  day  would  probably  not  exceed  eight 
or  ten  degrees. 

The  modification  of  the  winter  temperatures  of  the 
United  States,  through  its  topographical  features,  was 
incidentally  referred  to  on  page  106,  and  may  now  be 
slightly  enlarged  on  with  reference  to  the  distribution 
of  cold  waves. 

The  movement  of  any  low-area  storm  has,  as  a  neces- 
sary accompaniment,  the  indraughting  of  air  in  its 


212  AMERICAN   WEATHER. 

wake,  to  replace  that  drawn  spirally  inward  and  up- 
ward at  the  moving  storm-centre. 

.As  is  shown  on  Charts  XX.  and  XXI.,  the  low-area 
storms  of  the  United  States  most  frequently  develop 
on  the  slopes  to  the  eastward  of  the  summit  of  the 
Rocky  Mountains,  whence  they  move  to  the  Atlantic. 
If  the  country  over  which  the  storm-centre  passes  was 
a  level  plateau,  or  was  devoid  of  marked  breaks,  in  the 
shape  of  deep  valleys  and  high  mountain  ranges,  the 
quarter  from  which  this  air  wo  aid  flow  in  would  de- 
pend on  the  direction  in  which  the  storm-centre  was 
moving,  modified,  of  course,  by  the  law  of  cyclonic 
winds  and  by  deflection  due  to  the  daily  axial  rotation 
of  the  earth.  But  there  are  very  marked  topographi- 
cal features  in  the  United  States,  which  result  in  caus- 
ing to  advance  from  British  America  the  greater  part 
of  the  winds  following  in  the  wake  of  cyclonic  storms. 
The  Rocky  Mountain  range,  averaging  about  nine 
thousand  feet  in  elevation,  is  as  high  or  higher  than 
the  upper  strata  of  most  low-area  storms,  and  so  the 
air  current  cannot  be  drawn  from  the  westward.  Again, 
the  broad,  vast  valley  drained  by  the  Mississippi  de- 
scends with  a  gradual  and  substantially  unbroken  slope 
from  British  America  to  the  Gulf  of  Mexico,  so  that 
any  air  flowing  northward  must  be  considerably  re- 
tarded in  its  movement  by  the  great  friction  arising 
from  moving  over  continually  ascending  ground.  On 
the  other  hand,  the  air  from  British  America  passes  off 
gradually  descending  surfaces,  and  this  movement  is 
further  facilitated  by  the  air  being  dry  and  cold,  and 
hence  dense,  which  naturally  underruns  with  readiness 
the  lighter,  warmer  air  of  the  retreating  low  area. 

It  is  thus  evident  why  anti-cyclonic  areas,  especially 
such  as  cause  severe  cold  waves,  have  a  marked  ten- 
dency to  move  southward,  and  even  such  cold  waves  as 


AMEKICAN   WEATHEE.  213 

move  east,  with  their  centres  in  high  latitudes,  always 
affect  the  trans- Mississippi  region  to  points  much  far- 
ther south  than  occurs  in  the  eastern  part  of  the  coun- 
try. The  Rocky  Mountain  range  is  also  higher  than 
the  top  of  most  of  the  air  strata  which  form  cold 
waves,  and  thus  the  outskirts  of  these  waves  do  not 
overflow  into  the  tramontane  regions.  Such  waves 
as  prevail  westward  of  the  Rocky  Mountain  summit 
have  their  origin  in  localities  to  the  westward  or  north- 
westward, and  are  drawn  southward  by  the  passage  of 
low  areas  which  also  originate  in  the  Pacific  coast 
region. 

The  effect  of  even  low  mountain  ranges  in  protecting 
a  section  from  cold  waves,  as  occurs  in  regard  to  the 
greater  part  of  Arkansas  and  Northern  Louisiana,  is 
very  noticeable.  If  there  existed  a  transverse  moun- 
tain range  extending  from  the  Rocky  Mountains  to  the 
Mississippi  River,  Texas  and  other  regions  to  the 
southward  would  be  fully  protected.  The  Appalachian 
range  shelters  to  a  great  extent  Virginia,  the  Caro- 
linas,  and  Georgia,  which  are  often  entirely  spared  the 
severe  cold  waves  experienced  in  the  Ohio  Valley  and 
Tennessee. 

A  cold  wave  results  from  the  movement  of  a  strong 
anti-cyclonic  area  across  the  United  States,  and,  as  has 
been  pointed  out  in  a  previous  chapter,  these  areas 
have  three  different  paths  :  one  from  west  to  east  across 
the  great  lakes  to  New  England  ;  second,  a  due  south- 
erly translation  from  Manitoba  to  Texas,  whence  they 
drift  easterly  with  the  general  atmospheric  conditions  ; 
and,  third,  a  path  intermediate  between  the  two. 

It  is  not  to  be  inferred  that  every  anti-cyclone  causes 
a  cold  wave.  The  limitations  of  summer  temperatures 
are  such  that  even  the  northwest  portions  of  the  United 
States  are  rarely  subject  to  these  phenomena  in  that 


214  AMERICAN   WEATHER. 

season.  During  July  cold  waves  are  unknown  ;  and 
in  June  and  August  not  more  than  five  per  centum  of 
the  high  areas  are  marked  by  conditions  where  the 
abnormal  fall  of  temperature  exceeds  fifteen  degrees  in 
twenty-four  hours  and  at  the  same  time  falls  below 
forty  degrees  Fahrenheit. 

During  the  remaining  months  of  the  year  the  per- 
centages of  anti-cyclones  causing  cold  waves  rise  stead- 
ily from  twenty  per  centum  in  September  to  a  maxi 
mum  of  ninety  per  centum  in  January,  and  then  slowly 
decrease  to  about  twenty  per  centum  in  May.  During 
January,  in  the  extreme  northwestern  part  of  the 
United  States,  it  is  reasonable  to  expect  on  an  average 
one  cold  wave  in  every  five  days,  while  in  February 
and  March  they  recur  about  weekly. 

The  greater  part  of  the  anti-cyclones  which  cause 
cold  waves — probably  ninety  per  centum — are  outpours 
of  dry  air,  chilled  to  a  very  low  temperature  by  radia- 
tion over  the  barren  grounds  of  British  America. 
Without  doubt,  the  very  low  temperature  to  which  the 
air  falls  is  due  to  the  barren,  treeless  character  of  that 
country,  which  is  covered  with  scanty  vegetation  dur- 
ing summer  and  free  from  ice  or  snow  during  the  win- 
ter, so  that  the  radiation  from  the  bare  ground  pro- 
ceeds with  great  rapidity  during  the  long  winter  nights 
in  this  sub-arctic  region. 

The  cold  wave  occurs  not  with  the  centre  of  the  anti- 
cyclone, but  on  its  outskirts,  far  in  advance  of  the 
centre,  and  the  great  and  sudden  falls  of  temperature 
obtain  most  frequently  when  the  movement  of  a  low 
area  to  the  eastward  has  raised  in  its  passage  the  tem- 
perature of  the  adjacent  country  to  an  abnormal] y 
high  point. 

The  passage  of  cold  waves  eastward  is  coincident 
with  the  movement  of  high  areas,  as  set  forth  in  a  pre- 


AMERICAN  WEATttEU.  215 


ceding  chapter,  and  the  outskirts  of  these  anti-cyclones 
travel  on  an  average  from  Manitoba  to  Texas  within 
forty-eight  hours,  and  in  about  the  same  time  to  the 
St.  Lawrence  Valley  or  the  Middle  Atlantic  coast. 

Lieutenant  T.  M.  Woodruff  has  pointed  out  that  the 
most  decided  changes  of  temperature  obtain  from  3  P.M. 
.  (about  the  usual  hour  of  maximum  temperature)  of  one 
day  until  3  P.M.  of  the  day  following. 

As  yet  it  has  not  been  determined  with  absolute  ac- 
curacy what  conditions  must  obtain  to  induce  the  pas- 
sage of  cold  waves  (1)  to  the  southward,  (2)  to  the  east, 
or  (3)  to  an  intermediate  point  in  the  southeast.  The 
question  doubtless  depends  upon  the  relative  relation 
of  the  centre  of  the  anti-cyclone  to  that  of  some  cyclone 
far  distant. 

The  author,  from  considerable  personal  observation, 
is  inclined  to  the  opinion,  however,  that  the  easterly 
or  southerly  movement  of  any  anti-cyclonic  area,  suffi- 
ciently marked  to  cause  a  cold  wave,  depends  very 
largely  upon  the  general  direction  and  average  lati- 
tude of  the  path  followed  by  the  last  cyclonic  area 
that  has  passed  across  the  United  States.  The  very 
destructive  anti-cyclones  of  December,  1'880,  and  Jan- 
uary, 1886,  were  preceded  by  cyclonic  storms,  which 
moved  eastward  from  the  western  Gulf  in  paths  of 
unusually  low  latitude.  The  slow  process  of  develop- 
ment, and  the  equally  slow  movement  of  these  low- 
area  storms  to  the  eastward,  resulted  in  inducing  north- 
erly winds  in  the  northwestern  quadrant  for  a  number 
of  days,  during  which  time  enormous  quantities  of 
cold  air  must  have  been  drawn  from  sub-arctic  Amer- 
ica. In  consequence,  the  whole  lower  air  strata 
from  Dakota  to  Kansas  were  abnormally  cold  and  dry, 
conditions  which  facilitated  local  radiation,  and  still 
further  re-enforced  the  outflow  of  cold,  dry  air  to  re- 


216  AMERICAN  WEATHER. 

place  the  surface  strata  drawn  southward.  Similar 
conditions — that  is,  continued  northerly  winds — ob- 
tained in  rear  of  a  similar  low-area  storm  in  March, 
1888,  and  resulted  in  the  combined  cold  wave  and  bliz- 
zard which  wrought  so  much  devastation  and  injury 
to  Southern  New  England  and  the  vicinity  of  New 
York  City. 

On  the  other  hand,  it  is  noticed  that  many  of  the 
anti-cyclones — those  which  pass  easterly  across  the 
great  lakes— follow  in  the  wake  of  low-area  storms  of 
easterly  paths,  from  Minnesota  to  the  St.  Lawrence 
Valley,  in  a  comparatively  high  latitude.  During  the 
cyclone's  development  and  passage  warm  southerly 
and  easterly  winds  have  prevailed  over  the  United 
States,  which  winds  not  only  were  warmer  than  the 
local  air  strata,  but  also  brought  with  them  vast  quan- 
tities of  aqueous  vapor,  which,  being  set  free  by  conden- 
sation, likewise  tended  to  raise  the  temperature  of  the 
adjacent  general  atmosphere. 

The  following  are  among  the  most  remarkable  cold 
waves  that  have  occurred  in  late  years,  and  may  serve 
for  comparison  with  future  ones  in  the  United  States  : 

March  19t7i-22d,  1876  ;  causing  violent  northers  on 
the  Texas  coast,  with  winds  ranging  from  fifty  to  sixty 
miles  per  hour,  and  destructive  frosts  through  all  the 
Gulf  States.  In  the  northern  half  of  Florida  many 
orange  and  fruit  trees  were  destroyed,  and  all  early 
vegetables. 

January  \st-7th,  1879  ;  during  which  the  temper- 
ature fell  to  —60°  at  Battlefield,  N.  W.  T.,  to  —5°  near 
Washington,  25°  at  Jacksonville,  Fla.,  and  46°  on  the 
Bermudas. 

January  ^)tli-February  \st,  1879 ;  accompanied 
by  a  severe  snow-storm  in  Nebraska,  through  which 
thousands  of  cattle  later  died,  owing  to  lack  of  forage. 


AMERICAN  WEATHER. 

February  9t7i-14t7i,  1881  ;  affecting  Southern  Cali- 
fornia, Arizona,  and  Texas.  Ice  formed  at  Campo, 
CaL,  Indian ola  and  Eagle  Pass,  Tex.,  and  Mobile, 
Ala.  The  passage  of  this  high  area  caused  severe  bliz- 
zards in  Dakota,  Nebraska,  and  Kansas,  stopping  all 
travel,  destroying  many  thousands  of  cattle,  and  caus- 
ing great  suffering  among  the  people  for  want  of  food 
and  fuel. 

This  cold  wave  was  unprecedented  as  to  duration, 
severity,  and  prolonged  movement  to  the  southward. 
It  moved  rapidly  southward,  apparently  traversing 
the  Cordilleras,  through  Mexico,  as  Guatemala,  on  Feb- 
ruary 10th,  was  visited  by  a  frost  which  was  claimed, 
at  the  time,  to  be  the  heaviest  within  the  memory  of 
man.  Ice  formed  in  many  places,  while  coffee-trees 
were  damaged  and  sugar-cane  killed.  In  Guatemala 
the  value  of  crops  destroyed  was  estimated  to  be  over 
one  million  dollars. 

That  this  cold  wave  extended  so  far  southward  is 
doubtless  due  to  the  unusual  circumstance  that  a  low- 
area  storm,  whose  centre  could  not  be  definitely  located 
for  lack  of  reports,  evidently  prevailed  over  Northern 
Mexico  from  January  6th-8th.  It  passed  to  the  Gulf 
of  Mexico  the  night  of  January  8th,  9th,  1881,  and  was 
doubtless  followed  by  the  wave  described  above. 

March  2d-4t7i,  1881  ;  the  advance  of  this  anti-cy- 
clone following  closely  a  low-area  storm  caused  a 
severe  blizzard  in  Illinois,  Indiana,  Iowa,  Wisconsin, 
and  Michigan.  In  many  localities  the  storm  was  said 
to  be  the  most  severe  for  a  quarter  of  a  century.  The 
snowfall  was  generally  heavy,  so  that  the  violent 
winds  drifted  it  in  many  places  to  great  depths.  For 
several  days,  in  the  greater  part  of  the  States  named, 
the  roads  were  completely  blocked,  communication  im- 
possible, and  all  business  suspended.  Over  two  hun- 


218  AMERICAN  WEATHER. 

dred  tons  of  mail  matter  accumulated  at  Chicago,  as  all 
railroad  lines  to  the  West  were  closed.  This  blizzard 
entailed  an  enormous  amount  of  suffering  to  thousands 
from  lack  of  food  and  fuel  during  the  blockade.  Sim- 
ilar gales,  with  like  results,  were  experienced  in  these 
same  States  during  the  19th,  20th,  29th,  and  30th,  thus 
making  March,  1881,  a  memorable  month  for  snow 
blockades. 

January  llth-lfttTi,  1882.  The  Pacific  coast  region  is 
rarely  affected  by  severe  weather,  with  freezing  temper- 
atures and  general  snows,  and  this  anti-cyclone  was,  per- 
haps, the  most  remarkable  in  that  section  in  recent 
years.  It  followed  a  low-area  storm  which  had  devel- 
oped in  Arizona  to  the  south  westward  of  the  Rocky 
Mountains.  On  January  13th,  14th,  the  weather  in 
Central  and  Southern  California  was  the  severest  ever 
known  ;  heavy  snow  followed  by  freezing  temperatures. 
Ice  formed  almost  to  the  seacoast  on  the  Mexican 
border,  and  snow-flakes  fell  at  San  Diego.  At  Stock- 
ton ice  formed  an  inch  thick,  and  at  Merced  one  half 
inch  thick.  At  Fresno  the  temperature  fell  to  21°,  and 
at  Campo  (2500  ft.  elevation),  on  the  Mexican  border,  the 
minimum  was  6.5°.  The  unprecedented  _f all  in  snow, 
mentioned  on  page  160,  and  the  unusually  low  temper- 
atures did  great  injury  to  sub-tropical  plants  and  caused 
the  death  of  many  sheep. 

February  18th-2Qth,  1882  ;  a  cold  wave,  during  which 
the  temperature  fell  to  10°  at  Fort  Gibson,  a  fall  of 
fifty -five  degrees  in  twenty-four  hours,  followed  in 
Texas  by  a  fall  of  thirty-five  degrees  in  the  same  length 
of  time.  This  was  immediately  followed  by  a  second- 
ary high  area,  which  caused  falls  in  twenty-four  hours 
of  thirty  degrees  in  Texas  on  the  21st,  and  from  New 
York  to  North  Carolina  a  fall  of  twenty-five  degrees 
on  the  22d. 


AMERICAN  WEATHER. 

January  6th-12t7i,  1883 ;  an  anti-cyclone  inducing 
severe  northers,  with  velocities  of  nearly  sixty  miles 
of  wind  on  the  Texas  coast  and  freezing  temperatures 
to  include  the  northern  half  of  Florida. 

January  16t7i-2Qt7i,  1883  ;  during  this  cold  wave 
the  temperature  fell  to  twenty  degrees  below  zero  from 
the  eastern  part  of  Washington  Territory  southeast  to 
Colorado  and  Western  Kansas,  and  zero  temperatures 
occurred  as  far  south  as  Northern  Texas  and  the  north- 
ern half  of  Arizona.  This  cold  wave  was  marked  by  a 
severe  norther  at  Key  West,  with  thirty-three  miles 
of  wind  per  hour  and  a  temperature  of  55°.  The  en- 
tire eastern  country  had  a  temperature  below  freezing, 
except  the  South  Atlantic  and  East  Gulf  coasts.  This 
wave  caused  immense  suffering  to  the  people  of  the 
whole  country,  killed  a  large  amount  of  stock,  and  with 
the  preceding  one  made  January,  1883,  from  the  Mis- 
sissippi Valley  to  the  Rocky  Mountains,  from  eight  to 
twelve  degrees  colder  than  the  mean. 

January  \st-3d,  1884  ;  this  wave  caused  freezing 
temperatures  from  Texas  eastward  to  Northwestern 
Florida.  The  mean  minimum  temperatures  through 
Ohio  were  sixteen  degrees  below  zero,  in  Pennsylvania 
among  the  lowest  recorded  zero  temperatures  over  all 
of  Tennessee,  and  freezing  temperatures,  which  in- 
jured orange  groves,  occurred  as  far  south  as  Mana- 
tee, Sanford,  and  Limona,  Fla.  The  minimum  temper- 
atures over  Montana,  Dakota,  Minnesota,  the  central 
valleys  and  Southern  States  were  generally  the  lowest 
recorded  in  fourteen  years. 

January  3d,  1885  ;  marked  by  a  minimum  tempera- 
ture of  —63.1°,  the  lowest  ever  recorded  in  the  United 
States  at  Poplar  River,  Mont. ;  it  caused  falls  of  tem- 
perature during  the  twenty-four  hours,  ranging  as  great 
as  thirty- seven  degrees  in  the  lower  lake  region,  forty 


220  AMERICAN   WEATHER. 

degrees  in  Tennessee,  thirty  degrees  on  the  Atlantic 
coast,  and  twenty-six  degrees  in  the  Gulf  States. 

January,  1886,  as  described  in  the  preceding  chapter. 
(See  Fig.  31.)  Temperatures  in  Montana  fell  from 
forty  to  fifty  degrees  in  advance  of  its  centre,  the 
most  sudden  changes  being  fifty-five  degrees  in  twenty- 
four  hours  at  Helena,  and  fifty  degrees  in  eight  hours 
at  Fort  Maginnis.  This  cold  wave  was  marked  in 
Texas  by  an  unprecedented  fall  of  temperature — fifty- 
four  degrees  in  less  than  eighteen  hours  at  Galveston, 
where  the  minimum  was  11°.  The  temperature  fell 
below  zero  at  Atlanta,  Ga.,  snow  extended  as  far  south 
as  Fort  Gatlin,  Orange  County,  Fla. — the  first  time  on 
record.  In  Georgia  the  Ogeechee  Lake  froze,  for  the 
first  time  as  far  as  is  known,  and  also  the  Oconee 
River.  Ice  formed  to  the  thickness  of  three  inches, 
and  several  persons  froze  to  death  at  or  near  Charles- 
ton, S.  C. 

February  §th-\\t~h,  1885  ;  during  which  the  tem- 
perature fell  in  twenty- four  hours  fifty -two  degrees  at 
Pittsburg  (forty-two  degrees  in  eight  hours),  from 
twenty-five  to  forty  degrees  in  the  West  Gulf  States, 
from  fourteen  to  twenty-seven  degrees  in  the  Missis- 
sippi Valley,  from  twenty  to  forty  degrees  in  the  lake 
region,  and  between  twenty  and  thirty  degrees  along 
the  Atlantic  coast  from  Florida  to  Maine.  This  cold 
wave  caused  the  lowest  temperatures  known  for  Feb- 
ruary in  many  years  in  Ohio,  Illinois,  Wisconsin,  and 
New  York. 

February  3d-5th,  1886  ;  a  very  severe  wave,  dur- 
ing which  the  temperature  was  below  freezing  along 
the  East  Gulf  coast  and  below  zero  from  New  England 
westward  to  Iowa.  The  minimum  temperatures  were 
generally  the  lowest  ever  observed  in  February  in  the 
Ohio  Valley,  Tennessee,  and  the  Middle  Atlantic  States. 


WEATHER. 

Marcli  20t7i-24t7i,  1885  ;  this  cold  wave  is  notable 
as  producing  unusually  low  temperatures  at  a  late  sea- 
son of  the  year.  It  caused  a  fall  in  twenty-four  hours 
of  about  twenty  degrees  through  the  Gulf  and  South 
Atlantic  States.  At  Escanaba,  Mich.,  a  temperature 
of  —25°  occurred  on  the  21st,  one  of  the  lowest  tem- 
peratures ever  recorded  in  March,  and  the  lowest  ever 
known  at  so  late  a  date.  The  Delaware  River  froze 
over  at  this  date  at  Easton,  Pa.,  and  the  Lehigh  at 
South  Bethlehem,  Pa.,  for  the  first  time  during  the 
winter,  and  all  canals  in  the  State  were  closed.  North 
and  East  rivers  at  New  York  City  were  filled  with 
large  quantities  of  ice,  obstructing  navigation  for  sev- 
eral days.  New  Haven  Harbor,  Conn. ,  and  the  Potomac 
River  at  Washington  both  froze  over.  Freezing  tem- 
peratures were  experienced  as  far  south  as  Pensacola, 
Fla.,  and  great  damage  was  done  to  early  vegetation  all 
through  the  Gulf  and  South  Atlantic  States. 

February  \Wi-\St7i,  1887  ;  two  anti-cylones.  Par- 
ticularly felt  in  Missouri,  Montana,  Colorado,  and 
Northern  Texas,  in  all  of  which  sections  the  tempera- 
ture sank  from  forty  to  fifty  degrees  in  eight  hours, 
and  from  fifty-two  to  sixty  degrees  in  twenty-four 
hours.  At  Lamar,  Mo.,  the  fall  in  nine  hours  was 
fifty-eight  degrees,  and  in  twenty- four  hours  sixty  and 
three-tenth  degrees — one  of  the  largest  ever  recorded 
in  the  United  States  for  that  period.  For  nearly  three 
weeks  rail  communication  was  blockaded  in  South- 
eastern Dakota  and  telegraphic  and  rail  communica- 
tion interfered  with  in  Minnesota  and  Northern  Michi- 
gan. 

February  1st -3d,  1887  ;  the  advance  of  which  was 
marked  in  Montana  by  falls  of  temperatures  of  from 
forty -five  to  fifty-five  degrees  in  twenty-four  hours, 
with  drifting  snow,  causing  in  that  Territory  the  loss 


222  AMERICAN  WEATHER. 

of  a  large  number  of  cattle  from  starvation,  and  delay- 
ing for  many  days  all  communication  by  stage  and 
rail  line's.  In  Dakota  the  winds  were  high,  snow 
heavy,  and  the  temperature  extremely  low,  causing  a 
large  number  of  cattle  to  perish  by  exposure,  or  later 
by  starvation,  owing  to  the  ground  being  covered  with 
crusted  snow. 

March  3d-6t7i,  1887 ;  this  anti-cyclone  was  marked 
by  freezing  temperatures  as  far  south  as  the  36th 
parallel,  and  zero  temperatures  from  Dakota  to  North- 
ern New  England.  In  its  passage  across  the  last- 
named  section  the  temperatures  fell  in  New  Hamp- 
shire and  Maine  with  remarkable  rapidity,  the  changes 
ranging  from  fifty  to  seventy  degrees  from  the  noon 
maxima  of  March  4th  to  the  morning  minima  of  the 
5th.  At  Berlin  Mills,  N.  H.,  the  change  in  this  time 
amounted  to  sixty-seven  degrees,  and  at  West  Milan, 
N.  H.,  was  seventy-one  degrees. 

March  24th-30t7i,  1887 ;  this  cold  wave  was  unusually 
severe,  considering  the  lateness  of  the  season,  in  Ala- 
bama, Georgia,  North  and  South  Carolina.  Very  severe 
frosts  were  experienced  in  the  interior  of  all  these 
States,  where  the  early  fruits  and  crops  were  damaged 
extensively. 

BLIZZARDS. 

Among  one  of  the  first  to  mention  the  'blizzard  was 
Henry  Ellis,  who  made  a  voyage  to  Hudson  Bay  in 
the  ship  California,  in  the  year  1746,  and  wintered 
near  York  Factory.  He  speaks  of  the  northwest  wind 
as  being  exceedingly  trying,  not  only  on  account  of 
the  intense  cold,  but  owing  to  the  air  being  filled  with 
fine,  hard  particles  of  snow,  which  made  it  almost  un- 
bearable. The  first  use  of  this  term  by  the  Signal 
Service  was  in  one  of  its  publications,  The  Monthly 
Weather  Review,  in  December,  1876. 


AMERICAN   WEATHER.  223 

One  of  the  most  severe  blizzards  within  the  past 
quarter  of  a  century  was  that  which  occurred  in  an 
unusually  late  period  of  the  year  in  Dakota,  from 
April  13th-16th,  1873,  and  in  connection  with  or 
shortly  after  this  storm  the  use  of  the  word  became 
tolerably  frequent  in  the  northwestern  parts  of  the 
United  States,  to  indicate  such  cold  anti-cyclonic 
storms  as  are  attended  by  drifting  snow. 

The  Dakota  blizzard  of  April,  1873,  was  of  the  most 
violent  character,  as  is  shown  by  the  few  recorded  ob- 
servations. The  wind  blew  at  Yankton,  Dak.,  from 
the  13th  to  the  16th,  inclusive,  for  a  continuous  period 
of  nearly  100  hours,  at  an  average  velocity  of  thirty- 
nine  miles  per  hour,  and  on  April  15th  the  velocity  for 
the  entire  twenty-four  hours  was  over  fifty-two  miles 
per  hour.  This  hurricane-like  wind,  unprecedented  in 
the  interior  of  the  United  States  for  continued  vio- 
lence, was  accompanied  by  fine  drifting  sriow,  which 
was  like  sand,  and  so  filled  the  air  that  one  could  not 
see  a  dozen  yards.  The  Seventh  Regiment  of  United 
States  Cavalry  was  camped  in  Yankton  at  the  time, 
and  for  more  than  forty-eight  hours  officers  and  men 
alike  were  obliged  to  seek  shelter  in  the  houses  of  the 
citizens.  Business  of  all  kinds  was  necessarily  sus- 
pended, travel  impossible,  the  suffering  and  damage 
prolonged  and  great.  Large  numbers  of  cattle  were 
frozen  to  death.  A  considerable  number  of  persons 
were  badly  frozen,  but,  fortunately,  deaths  were  few, 
owing  to  the  gradual  increase  in  the  violence  of  the  storm 
and  the  fact  that  the  Territory  most  affected  was  then 
thinly  populated.  It  doubtless  exceeded  in  violence 
and  duration  the  more  fatal  blizzard  of  January,  1888, 
when  scores  of  human  beings  perished  in  Dakota  and 
Nebraska. 

The  most  disastrous  blizzard  ever  known  in  Montana, 


224  AMERICAN   WEATHER. 

Dakota,  Minnesota,  Kansas,  and  Texas,  occurred  on 
January  llth,  1888.  The  change  in  the  direction  of 
the  wind  and  the  fall  in  the  temperature  was  more  sud- 
den than  usual.  Although  the  greatest  violence  of  the 
storm  was  of  short  duration,  yet  it  was  most  destructive 
in  its  effects  in  Middle  and  Southern  Dakota,  owing  to 
the  fact  that  the  change  in  wind,  weather,  and  temper- 
ature came  suddenly  in  the  middle  of  a  comparatively 
warm  and  pleasant  day  when  many  were  away  from 
shelter.  The  loss  of  life  was  probably  nearly  one  hun- 
dred persons,  although  the  exact  figures  are  not  known. 
High  winds  ranging  from  thirty  to  fifty  miles  per  hour 
occurred,  with  falling  and  drifting  snow,  which,  in  ad- 
dition to  the  great  loss  of  human  life,  caused  the  de- 
struction of  herds  of  cattle  and  an  enormous  amount 
of  suffering  to  entire  communities.  At  Helena,  Mont., 
the  temperature  changed  with  unprecedented  rapidity, 
falling  fifty  degrees  in  four  and  one  half  hours  and 
sixty-four  degrees  in  less  than  eighteen  hours.  Com- 
munication by  rail  and  otherwise  was  either  seriously 
delayed  or  entirely  suspended  for  several  days  in 
Northern  Dakota  and  Minnesota.  At  Crete,  Neb. ,  the 
temperature  fell  eighteen  degrees  in  three  minutes,  and 
snow  drifted  so  violently  as  to  render  all  travel  dan- 
gerous. At  Galveston,  on  the  15th,  the  temperature 
was  below  the  freezing  point,  while  the  air  was  filled 
with  fine  drifting  snow  or  freezing  mist,  which,  owing 
to  the  influence  of  a  wind  of  forty  miles  per  hour,  cut 
like  drifting  sand  and  coated  everything  with  ice.  At 
Rio  Grande  City  and  Brownsville,  Tex.,  the  wind  was 
violent  and  the  temperature  fell  nearly  forty  degrees 
in  eight  hours.  The  cold  rain  changed  to  snow  and 
sleet,  covering  everything  with  ice,  and  causing  great 
suffering. 
A  peculiar  feature  of  this  blizzard  was  its  extension 


AMERICAN    WEATHER.  225 

in  the  shape  of  a  cold  wave,  without  snow,  however, 
into  California.  Slush  ice  was  seen  in  the  river  at 
Sacramento  for  the  first  time  since  1854,  while  ice 
formed  in  San  Francisco  to  the  thickness  of  half  an 
inch.  At  and  near  Los  Angeles  ice  and  killing  frost 
were  general,  and  even  at  San  Diego  there  was  light 
frost  and  a  thick  film  of  ice  in  exposed  places. 

The  most  remarkable  blizzard  in  the  eastern  part 
of  the  United  States  was  that  of  March  llth-14th, 
1888.  The  heavy  snow  and  high  winds  attending 
it  completely  interrupted  telegraphic  and  railway 
communication  in  New  Jersey,  Eastern  Pennsylvania, 
and  the  southern  half  of  New  York  and  New  England. 
Business  was  entirely  suspended  in  these  sections  dur- 
ing the  12th  and  13th.  The  advance  of  the  anti- 
cyclone was  marked  by  a  sudden  and  rapid  fall  of  tem- 
perature, heavy  snow,  and  violent  northwesterly  winds, 
which  not  only  made  travel  dangerous  but  almost  im- 
possible. For  four  days  the  average  wind  velocity 
throughout  the  sections  named  ranged  from  twenty  to 
twenty-five  miles  per  hour,  and  at  times  attained  velo- 
cities varying  from  fifty  to  seventy  miles.  It  has  been 
shown  by  Prof.  Upton  that  the  snow  was  exceedingly 
heavy,  averaging  probably  forty  inches  or  more  over 
Southeastern  New  York  and  Southern  New  England. 
The  violent  winds  filled  the  air  for  one  or  two  days 
with  blinding  snow,  which  drifted,  under  favorable  cir- 
cumstances, to  a  depth  of  ten  or  fifteen  feet  in  New 
York,  New  Haven,  and  adjacent  cities.  It  was  five 
or  six  days  before  regular  communication  was  re-estab- 
lished and  ordinary  business  resumed.  Many  persons 
who  faced  the  storm  were  badly  frozen  or  prostrated 
by  the  low  temperature,  drifting  snow,  and  high  winds, 
and  the  loss  of  life  from  this  cause,  directly  or  indi- 
rectly, was  considerable.  New  York,  Philadelphia, 


226  AMERICAN  WEATHER. 

and  Boston  were  completely  isolated,  and  the  only  ad- 
vices possible  for  one  or  two  days  from  the  latter  city 
were  via  London,  England,  by  cable.  At  Delaware 
Breakwater  only  thirteen  out  of  forty  vessels  escaped 
serious  damage  or  destruction,  and  thirty  or  more 
lives  were  lost. 

The  maritime  interests  suffered  from  this  blizzard  to 
the  extent  of  over  one  half  a  million  dollars,  while  the 
losses  by  railroads  and  other  business  interests  could 
not  be  accurately  estimated,  but  must  have  aggregated 
several  millions  of  dollars.  The  storm  was  quite  as 
severe  as  any  blizzard  of  the  Northwest,  and  much 
farther  reaching  in  working  damage  and  destruction, 
owing  to  its  occurrence  in  so  densely  populated  a 
region.  The  highest  recorded  winds  were  as  follows  : 
Eastport,  Me.,  seventy- two  miles  for  a  single  hour, 
twenty-seven  miles  for  ninety-six  consecutive  hours  ; 
Block  Island,  seventy  miles  and  thirty-two  miles  ;  New 
York  City,  fifty  miles  and  thirty-two  miles  ;  Phila- 
delphia, sixty  miles  and  twenty-six  miles. 

It  must  not  be  imagined  that  this  storm  is  un- 
equalled in  the  annals  of  this  or  other  countries.  Eng- 
land and  France  are  thought  by  many  to  be  entirely 
free  from  such  variable  weather  conditions  ;  but  such 
is  not  the  case.  On  January  18th,  19th,  1881,  similar 
storm  conditions  obtained  in  England  and  France,  with 
more  disastrous  results,  and  the  description,  except 
the  larger  number  of  deaths,  would  be  strictly  applic- 
able to  the  American  storm. 

The  gale  was  particularly  severe  on  the  east  coast  of 
England,  accompanied  by  a  heavy  fall  of  snow  through 
the  18th  and  till  about  noon  of  January  19th.  The 
amount  of  snow  over  the  whole  southern  portion  of 
the  country  was  very  great.  Snow-drifts  of  four  to 
twelve  feet  were  general  throughout  Southern  Eng- 


AMERICAN   WEATHER.  227 

land.  The  snow  was  so  drifted  by  the  wind  that  com- 
munication of  every  kind  was  entirely  disorganized, 
and  it  was  more  than  a  week  before  the  railway  and 
postal  arrangements  throughout  England  and  Wales 
were  restored  to  their  usual  regularity.  The  interrup- 
tion to  business  was  further  increased  by  the  large 
number  of  telegraph  wires  broken  by  the  gale.  The 
snowfall  in  the  Isle  of  Wight  and  in  South  Hampshire 
was  altogether  unprecedented  in  recent  times.  The 
loss  of  life  in  England  and  Wales,  entirely  due  to  the 
snow,  was  estimated  at  100  persons,  and  the  amount  of 
distress  occasioned  by  the  stoppage  of  supplies  of  food 
and  fuel  was  almost  incalculable. 

In  France  as  far  south  as  Paris  the  snowstorm  was 
also  very  severe,  and  caused  serious  delays  of  mails 
and  other  business.  Hundreds  of  market- wagons  were 
abandoned  in  the  heavy  drifts,  and  many  of  the  streets 
of  Paris  were  completely  blocked.  At  Lilte,  France, 
many  houses  were  damaged  and  railroad  travel  com- 
pletely suspended. 


CHAPTER  XVII. 

TORNADOES. 

THE  passage  of  cyclonic  storms  across  the  United 
States  is  occasionally  marked  by  winds  of  the  most 
violent  character,  which  are  known  under  the  name  of 
"  tornadoes."  There  is  no  other  part  of  the  globe 
which  is  as  liable  to  tornadoes  as  certain  portions  of 
the  United  States. 

As  has  been  pointed  out,  disturbances  of  the 
equilibrium  of  the  atmosphere,  in  connection  with 
cyclonic  storms,  take  place  in  a  manner  more  nearly 
horizontal  than  vertical,  the  currents  passing  spirally 
inward  and  upward.  In  whirlwinds  and  tornadoes 
(for  whirlwinds  may  be  considered  incipient  tornadoes) 
the  peculiarity  of  this  disturbance  is  that  it  occurs  in 
a  manner  more  nearly  vertical  than  horizontal.  Since 
tornadoes,  hail-storms,  and  thunder-storms  are  all 
in  the  same  advance  quadrants  of  low  areas,  and  all 
likewise  travel  with  greater  velocity  than  the  general 
storm  centre,  it  appears  probable  that  the  tornado  is  an 
intense  development  of  thunder  and  hail- storm  condi- 
tions, in  which  the  enormous  force  generated  by  the 
disruption  of  very  unstable  atmospheric  conditions  is 
applied  to  the  development  of  violent  whirlwinds,  in- 
stead of  spending  itself  in  the  formation  of  hail  or  in 
the  inducing  of  violent  and  opposing  electrical  condi- 
tions. 

Conclusions  relative  to  the  paths  and  characteristics 
of  American  tornadoes  have  been  largely  drawn  from 


AMERICAN   WEATHER.  229 

the  studies  of  Lieutenant  John  P.  Finley,  Signal  Corps, 
whose  researches  and  compilations  have  elucidated 
some  points  before  unknown  or  doubtful,  and  no  other 
person  can  be  accorded  greater  credit  for  collecting  and 
arranging  data  respecting  these  storms.  Finley' s  re- 
searches and  collection  of  data  have  shown  clearly  what 
had  been  occasionally  noted  before,  that  tornadoes  do 
not  occur  in  the  immediate  vicinity  of  the  centre  of  a 
cyclonic  storm,  but  that  they  bear,  however,  a  definite 
and  tolerably  fixed  relation  to  the  centre,  and  occur  at 
a  distance  of  several  hundred  miles  to  the  southeast  of 
such  centre.  Marked  by  sharp,  decided  contrasts  of 
temperatures  and  dew-points,  preceded  by  warm,  south- 
erly, and  followed  by  cold,  northerly  winds,  these 
areas  of  low  pressure  lie  on  the  northwestern  edge  of 
the  tornado  region.  Tornadoes  always  occur  in  con- 
nection with  strong  warm  winds,  while  th£  atmosphere 
is  not  only  nearly  or  quite  saturated,  but  also,  from  its 
high  temperature,  contains  an  abnormally  large  amount 
of  aqueous  vapor. 

It  appears  certain  that  a  state  of  unstable  atmospheric 
equilibrium  exists,  which  most  likely  is  due  to,  or  co- 
existent with,  very  rapid  diminutions  of  temperature 
with  altitude,  thus  causing  vertically  very  large  tem- 
perature gradients  and  marked  contrasts  of  vapor 
conditions.  In  such  case,  the  presence  of  strong, 
warm,  moist  winds  produces  conditions  wherein  the 
strata  of  the  lower  atmosphere  is  liable  to  sudden  and 
violent  changes.  In  connection  with  such  rapid  trans- 
ference of  air,  it  requires  only  a  slight  predisposing 
cause  to  set  up  a  gyratory  motion,  and  thus  induce 
violent  winds,  known  as  tornadoes.  When  this  cur- 
rent is  once  set  in  motion,  it  naturally  propagates 
itself  along  such  line  and  in  such  direction  as  similar 
unstable  atmospheric  conditions  may  chance  to  ihen 


230  AMERICAN   WEATHER. 

prevail.  It  is  noticeable  that  this  gyratory  motion, 
as  indicated  by  the  general  formation  of  the  tornado 
cloud,  forms  in  the  upper  air  strata  and  gradually  de- 
scends to  the  earth  ;  thus  affording  proof  that  the 
gyratory  motion  is  initiated  in  the  upper  air  strata, 
where  the  air  currents  are  necessarily  of  far  greater 
velocity  than  at  the  surface  of  the  earth,  and  the  un- 
stable conditions  naturally  more  marked  than  below. 

According  to  Ferrel,  the  funnel-  shaped  cloud — which 
is  characteristically  tornadic,  and  is  seen  suspended 
from  the  lower  surface  of  the  undisturbed  stratum  of 
clouds —is  the  water- spout  which  every  tornado  must 
have  in  its  central  part. 

It  is  also  possible  that  a  tornado  is  the  extending 
downward  of  the  violent  movements  of  the  atmo- 
sphere which  normally  exist  in  the  upper  air  strata. 
The  velocity  of  the  winds  on  Mount  Washington  causes 
us  to  infer  that  it  is  not  unreasonable  to  expect  that,  in 
connection  with  severe  cyclonic  storms,  the  winds  at 
the  centre  of  a  severe  storm  blow,  at  an  altitude  of  five 
or  six  thousand  feet,  with  velocities  differing  not  far 
from  those  occurring  in  connection  with  tornadoes. 

Ferrel  believes,  and  with  good  reason,  that  a  tornado 
cannot  occur  unless  there  is  both  a  state  of  unstable 
equilibrium  of  the  air  and  a  gyratory  motion  with  ref- 
erence to  a  centre  ;  and  when  these  principal  conditions 
obtain,  the  slight  initial  disturbance  to  cause  the  tor- 
nado is  rarely  wanting. 

As  has  been  set  forth  in  preceding  chapters,  the 
progressive  motion  of  cyclonic  storms  depends  largely, 
if  not  entirely,  upon  the  velocity  and  direction  of  up- 
per air  currents.  It  has  also  been  stated  that  condi- 
tions of  cloud  and  rain,  which  engender  or  facilitate  a 
cyclonic  storm  system,  are  far  in  advance  of  the  centre, 
generally  toward  the  east,  It  thus  seems  possible  that 


AMERICAN  WEATHEB.  231 

the  centre  of  the  cyclonic  storm  does  not  advance  across 
the  country  in  a  vertical  position,  but,  as  advanced  by 
Ferrel,  rather  at  a  marked  inclination,  the  upper  por- 
tion of  the  storm  being  considerably  in  advance  of  the 
storm  centre  at  the  surface  of  the  earth.  Such  an  in- 
clination to  the  centre  of  the  storm  would  facilitate 
severe  local  storms  or  tornadoes  at  a  considerable  dis- 
tance in  advance  of  the  storm  itself,  and  since  such 
violent  storms  do  occur  locally  in  advance  of  all  violent 
cyclonic  storms,  it  may  be  possible  in  case  of  tornadoes 
that  the  inclination  is  very  marked.  Probably  these 
storms  occur  in  the  southeasterly  quadrants  with 
greater  violence,  as  tornadoes,  simply  because  the  larger 
amount  of  aqueous  vapor  in  the  air  causes  conditions 
more  marked  and  unstable  than  could  occur  in  the 
northern  or  western  quadrants. 

From  what  has  been  written  the  reader  may  correctly 
infer  that  the  cause  and  development  of  tornadoes  in- 
volve some  points  not  yet  definitely  elucidated. 

The  months  of  greatest  tornado  frequency  in  the 
United  States,  as  shown  by  Finley,  are  May,  April, 
June,  and  July,  in  order  named.  The  hours  of  great- 
est frequency  during  the  day  are  from  3.30  to  5  P.M., 
just  after  the  warmest  part  of  the  day,  when  warm  as- 
cending air  currents  are  most  liable  to  meet  cooler  de- 
scending ones. 

In  the  United  States  3000  persons  have  been  killed 
and  as  many  more  injured  by  these  storms.  As  far  as 
the  data  goes,  the  loss  of  life  has  been  greatest  in  rela- 
tive order  in  States  as  follows  :  Missouri,  Mississippi, 
Iowa,  Illinois,  Minnesota,  Wisconsin,  and  Ohio.  The 
loss  of  property  aggregates  scores  of  millions  of  dollars, 
and  has  been  fixed,  in  round  numbers,  as  follows  :  Ohio, 
over  eight  millions  of  dollars  ;  Minnesota,  six  millions  ; 
Missouri,  three  millions  ;  Mississippi,  two  millions ; 


232 


AMERICAN  WEATHER. 


Iowa,  one  million  and  one  half  ;  Wisconsin,  over  one 
million. 

LIST    OF     TWENTY-FIVE    OF    THE    MOST    DESTRUCTIVE 
TORNADOES  IN  THE   UNITED   STATES. 


No 
Per 

.of 
sons 

a 

to 

2-3 

STATE. 

County. 

Date. 

i 
s 

1 
1 

It 
II 

3  OJ 

PQ 

£1 

og 

sS 
fa 

Miss.  . 

May  7,  1840. 

317 

109 

$1  260  000 

Miss.  . 

Adams  

June  16,  1842. 

500 

... 

Ala 

Colbert  

Nov.  22,  1874. 

10 

30 

100 

Wis  .  . 

Iowa  

May  23,  1878. 

30 

Mo..  . 

Ray  

June  1,  1878. 

13 

70 

100 

Conn 

New  Haven 

Aug  9    1878. 

34 

28 

160 

2  000  000 

Mo.  .  . 

Miss  . 

Barry,    Stone,  Web- 
ster  and  Christian. 
Noxubee  

j.  April  18,  1880. 
April  25  1880. 

101 
9,9, 

600 

79, 

55 

1,000,000 
100  000 

Texas. 

May  28,  1880. 

40 

83 

49 

Iowa 

Poweshiek      .  .      . 

June  17  1882 

100 

300 

260 

1  000  000 

Minn 

Brown     .       

July  15  1881 

11 

65 

300 

400  000 

Mo.  .. 
Miss  .  . 

Wis.. 

Henry  and  Saline.  .  . 
Kernper,        Copiah, 
Simpson,  Newton, 
and  Lauderdale..  . 
Racine 

April  18,  1882. 
[  April  22,  1883. 
May  18  1883 

8 
51 
16 

150 
200 
100 

51 
100 
52 

150,000 
300,000 
175  000 

Minn  . 
Ark... 

Dodge  and  Olmstead 
Izard,     Sharp      and 
Clay  

Aug.  21,  1883. 
[  Nov.  21,  1883. 

26 
5 

80 
162 

400 
60 

700,000 
300,000 

N.C.. 

Richmond  and  Har- 

j-  Feb.  19,  1884. 

18 

125 

55 

Dak... 

Miner,     Lake      and 

A/ri«TiaV»aVia 

> 
!•  July  28,  1884. 

15 

18 

100 

Minn.. 

Rock,        Hennepin, 
Ramsey  and  Wash- 
ington 

Wis... 

St.  Croix,  Polk,  Bar- 
row, Chippewa  and 
Price 

\  Sept.  9,  1884. 

b 

Vt> 

305 

4,000,000 

N  J 

Camden     

Aug  3  1885. 

6 

100 

500 

500  000 

Ohio  . 

Fayette  

Sept.  8,  1885. 

6 

100 

300 

500  000 

Minn  . 

Benton  and  Stearns.. 

April  14,  1886. 

74 

)  9,7 

136 

138 

385,000 
1  000  000 

Ohio  . 
Kan 

Greene  and  Huron.  . 
Prescott  

May  12,  1886. 
April  21,  1887. 

y  30 

30 

'9,37 

85 
330 

300,000 
1,000,000 

AMERICAN   WEATHER.  233 

Chart  No.  XXIV.  shows  the  distribution  of  tornadoes 
in  the  United  States.  This  chart,  originally  prepared 
by  Lieutenant  Finley,  shows  the  distribution  only  in 
a  general  manner.  Data  of  this  kind  is  always  in- 
complete, especially  in  the  thinly  settled  portions  of 
the  country,  and  so  the  lines  of  equal  frequency  are 
somewhat  uncertain  ;  but  there  can  be  no  doubt,  how- 
ever, that  the  relative  frequency  is  greatest  in  the 
valleys  of  the  lower  Missouri  and  of  the  upper  Missis- 
sippi. It  has  been  demonstrated  by  Ferrel  that  this 
region  is  theoretically  liable  to  tornadoes  owing  to  the 
counter- currents  of  cold  air  from  the  northward,  and 
warm,  very  moist  southerly  winds  from  the  Gulf  of 
Mexico,  which  latter  currents  tend  to  cause  an  unstable 
state  of  the  atmosphere. 

Finley  has  pointed  out  that  tornadoes  rarely  if 
ever  occur  west  of  the  100th  meridian,  in  which  regions 
the  lack  of  aqueous  vapor  and  the  want  of  intensity  in 
other  phenomena  of  cyclonic  storms  furnish  sufficient 
reasons  for  their  non-existence. 

The  tornado  follows  a  definite  path,  which,  as  a  gen- 
eral rule  (about  eighty  per  centum),  is  from  the  south- 
west toward  the  northeast.  About  ten  per  centum  move 
from  northwest  to  southeast.  The  path  of  greatest 
violence  varies,  as  a  general  rule,  between  one  hundred 
and  six  hundred  yards  in  width,  and  from  one  to  fifty 
miles  in  length.  The  progressive  movement  of  the 
tornado  is  very  rapid,  being  rarely  under  twenty 
miles  an  hour  or  over  fifty  miles,  and  the  time  taken 
in  the  passage  of  the  immediate  centre  is  between  five 
and  ten  minutes. 

The  violence  of  the  tornado  is  too  familiar  to  need 
elaboration.  Winds  which  uproot  or  twist  off  the 
largest  trees,  unroof  or  destroy  the  most  stable  build- 
ings, lift  the  heaviest  locomotives  from  the  railway 


234  AMERICAN  WEATHER. 

track,  and  even  upraise  and  carry  from  their  founda- 
tions large  iron  bridges,  can  be  better  imagined  than 
described. 

One  of  the  most  remarkable  and  best  known  torna- 
does in  the  United  States  is  the  Marshfield,  Mo., 
tornado,  which  occurred  April  18th,  1880.  The  town 
of  Marshfield  was  nearly  destroyed,  and  ninety -two  of 
its  inhabitants  perished  from  this  terrible  storm.  On 
February  9th,  1884,  an  unparalleled  series  of  tornadoes 
occurred  from  Mississippi,  Tennessee,  Kentucky,  and 
Illinois,  eastward  to  Virginia,  North  Carolina,  South 
Carolina,  and  Georgia.  There  were  more  than  sixty 
separate  tornadoes  after  10  A.M.  of  that  disastrous  day. 
Over  ten  thousand  buildings  were  destroyed,  eight 
hundred  people  killed,  and  twenty-five  hundred 
wounded. 

Waterspouts  not  infrequently  occur  at  sea,  and  these 
phenomena  may  be  considered  as  incipient  tornadoes 
of  comparatively  feeble  force.  They  are  sufficiently 
powerful  at  times  to  disable  or  destroy  vessels,  though 
such  cases  are  comparatively  rare. 


CHAPTER   XVIII. 

HAIL,    THUNDER,    AND   DUST   STORMS. 

IN  addition  to  regular  cyclonic  storms  and  tornadoes, 
which  have  been  discussed  in  preceding  chapters,  there 
are  other  atmospheric  disturbances,  generally  known 
as  local  storms,  such  as  hail,  thunder,  and  dust  storms. 
These  atmospheric  disturbances  are  almost  invariably 
connected  with  the  passage  of  some  cyclonic  centre 
across  the  country,  and  can  be  considered  local  only  to 
the  extent  that  the  violent  manifestations  do  not  cover 
the  entire  area  of  the  country,  but  are  experienced  in 
patches  or  bands. 

Professor  Hazen's  investigations  show  that  both  hail 
and  thunder  storms  have  in  general  the  same  relative 
position  to  areas  of  low  pressures  as  do  tornadoes. 
Hail-storms  are  most  frequent  in  the  southeast  quad- 
rant, about  two  hundred  miles  in  advance,  while  thun- 
der-storms without  hail  are  about  twice  as  far  distant 
from  the  low  centre. 

Storms  of  hail,  unlike  those  of  rain,  do  not  cover  the 
country  universally,  but  the  hail-storm  follows,  like 
the  tornado,  a  path  whose  breadth  is  very  narrow  com- 
pared with  its  length.  It  very  frequently  occurs  that 
hail-storms  pass  over  certain  districts  in  parallel  bands, 
between  which  rain  only  and  no  hail  falls. 

Perhaps  the  most  remarkable  hail-storm  on  record 
was  that  of  July  13th,  1788,  which  passed  from  Tou- 
raine,  France,  to  Belgium.  The  mean  interval  between 
the  bands  was  twelve  miles,  while  the  western  hail 


236  AMERICAN  WEATHER. 

band  had  a  width  of  ten  miles  and  a  total  length  of 
42Q  miles,  and  the  eastern  band  a  width  of  five  miles 
and  a  length  of  500  miles.  Over  one  thousand  com- 
munes in  France  suffered  from  this  storm,  and  property 
valued  at  $5,000,000  was  destroyed. 

On  May  9th,  1865,  a  severe  hail-storm  followed  a 
path  from  forty-five  to  sixty  miles  in  width,  from  Bor- 
deaux, France,  to  Belgium.  In  the  arrondissement  of 
St.  Quentin  hail  fell  in  such  quantities  that  it  did  not 
disappear  for  over  four  days.  In  one  place  a  mass  of 
ice,  which  formed  from  the  hail,  was  said  to  be  a  mile 
and  a  quarter  long  and  about  two  fifths  of  a  mile 
broad,  amounting  to  21,000,000  cubic  feet. 

Dr.  Buist,  in  the  British  Association  report  for  1855 
on  hail-storms,  points  out  that  in  India  hail-storms 
occur  most  frequently  in  the  driest  months,  over  fifty 
per  cent  falling  during  March  and  April.  The  magni- 
tude of  the  hail- stones  and  the  severity  of  the  storms 
of  India  is  shown  by  that  which  occurred  in  the  Hima- 
layas north  of  the  Peshawur,  May  12th,  1853,  when 
eighty-four  persons  and  3000  oxen  were  said  to  have 
been  killed.  On  May  llth,  1855,  a  storm  occurred  at 
JSTaina  Tal,  29°  20'  N.,  80°  E.  Stones  as  large  as  cricket 
balls  fell,  some  weighing  ten  ounces,  and  one  or  two 
more  than  1.5  pounds  avoirdupois,  the  circumferences 
varying  from  nine  to  thirteen  inches. 

The  most  fatal  hail-storm  on  record  is  that  of  April 
30th,  1888,  at  Moradabad,  India.  There  is  no  question 
that  this  storm  directly  resulted  in  the  loss  of  more  than 
two  hundred  and  thirty  human  lives.  The  following 
account,  by  J.  S.  Macintosh,  C.S.,  was  furnished  the 
author  through  the  courtesy  of  John  Eliot,  Esq.,  Me- 
teorological Reporter  to  the  Government  of  India  : 

"  A  terrific  storm  of  hail  followed,  breaking  all  the 
windows  and  glass  doors.  The  verandas  were  blown 


AMERICAN  WEATHER. 

away  by  the  wind.  A  great  part  of  the  roof  fell  in, 
and  the  massive  pucca  portico  was  blown  down.  The 
walls  shook.  It  was  nearly  dark  outside,  and  hail-stones 
of  an  enormous  size  were  dashed  down  with  a  force 
which  I  have  never  seen  anything  to  equal.  As  soon  as 
the  storm  abated  I  went  out.  .  .  .  There  were  also 
long  ridges  of  hail  on  the  higher  ground  (of  the  race- 
course) one  or  two  feet  or  more  in  depth.  .  .  .  There 
is  not  a  single  house  in  the  civil  station  which  did  not 
sustain  the  most  serious  injury.  .  .  .  The  really  de- 
structive hail  seems  to  have  been  confined  to  a  very 
small  area,  about  six  or  seven  miles  around  Moradabad. 

"  Two  hundred  and  thirty  deaths  in  all  have  been  re- 
ported up  to  the  present  time.  The  total  number  may 
be  safely  put  as  under  two  hundred  and  fifty.  The 
majority  of  the  deaths  were  caused  by  the  hail.  Men 
caught  in  the  open  and  without  shelter  were  simply 
pounded  to  death  by  the  hail.  Fourteen  bodies  were 
found  in  the  race-course.  .  .  Most  of  the  deaths  were 
on  the  bare  and  level  plains  round  the  station,  where 
people  were  caught  unawares.  More  than  one  marriage 
party  were  caught  by  the  storm  near  the  banks  of  the 
river,  and  were  annihilated.  No  Europeans  were  killed. 
The  police  report  that  1600  head  of  cattle,  sheep,  and 
goats  were  killed." 

Mr.  Eliot  was  of  the  opinion  that  those  who  perished 
were  not  killed  directly  by  the  blows  of  the  hail-stones, 
but  by  being  knocked  down  by  the  wind,  were  buried 
in  the  hail,  and  perished  through  the  combined  effects 
of  cold  and  exhaustion. 

On  June  10th,  1879,  a  succession  of  violent  hail- 
storms passed  through  Eastern  Kansas  and  Western 
Missouri,  over  a  territory  340  miles  long  by  260  miles 
in  breadth,  travelling  from  northwest  to  southeast,  in 
narrow  belts  of  from  six  to  ten  miles  in  width. 


AMERICAN  WEATHE&. 

The  following  dates  indicate  the  most  remarkable  and 
destructive  hail-storms  that  have  occurred  in  the  United 
States  : 

July  30th,  1877.— In  the  Yellowstone  Yalley  hail- 
stones as  large  as  oranges  fell.  They  perforated  the 
tepees  of  the  Crow  Indians  and  killed  a  large  number 
of  ponies. 

June  5th,  1879. — Terrific  hail-storms  occurred  at 
West  Newton,  McKeesport,  Library,  Parker,  Philadel- 
phia, and  other  places  in  Pennsylvania  ;  Waltham, 
Mass.  ;  Hudson,  Mich.  ;  Atco  and  Yineland,  NT.  J.  ; 
Cleveland,  North  Lewisburg,  and  Norwalk,  O.  ;  Fort 
Hale  and  Yankton,  Dak.  At  Yankton  the  hail  was 
from  nine  to  twelve  inches  deep,  while  the  path  of  the 
storm  was  two  miles  wide  in  a  direction  from  southwest 
to  northeast. 

July  16t7i,  1879. — Severe  hail-storms  extended  in 
bands  from  Central  New  York  eastward,  to  include  the 
greater  parts  of  Massachusetts,  Rhode  Island,  and 
Connecticut.  At  Lanesboro,  Mass.,  stones  seven  inches 
in  circumference  fell. 

July  26th,  1880. — Violent  hail-storms,  with  stones 
from  six  to  ten  inches  in  circumference,  occurred  in 
Wisconsin.  The  path  near  Waupaca  was  from  south- 
west to  northeast,  and  two  miles  wide  ;  near  Stevens 
Point,  four  miles  wide  and  ten  miles  long.  Lambs  and 
sheep  were  killed  and  crops  totally  destroyed. 

June  24t7i,  1881. — A  very  destructive  hail-storm 
passed  over  a  section  of  country,  ten  miles  wide  and 
'twenty  miles  long,  in  the  Arkansas  River  Valley.  All 
grains,  grass,  and  vines  were  cut  down  level  with  the 
ground. 

July  26tk,  1881.— In  Cumberland  Co.,  Me.,  a  hail- 
storm moved  from  southwest  to  northeast — path,  two 
miles  wide  and  twenty  miles  long — the  most  violent 


AMERICAN   WEATHER.  239 

storm  since  1833,  when  a  similar  storm  followed  the 
same  path.  Stones  as  large  as  hens'  eggs  fell,  and 
in  such  quantities  that  twelve  hours  later  drifts  two 
feet  deep  were  visible. 

June  2d,  1881. — Very  violent  hail-storms  did  im- 
mense damage  in  Illinois.  Near  Mill  Creek  the  storm 
path  was  two  miles  wide  by  ten  miles  long.  Near 
Whitehall  the  storm  passed  from  northwest  to  south- 
east over  a  track  seven  miles  long  and  one  mile  wide. 
Drifts  of  hail  from  eight  to  twelve  inches  deep  were 
found  the  next  day,  and  some  of  the  stones  were  nearly 
the  size  of  goose  eggs. 

June  3d,  1881. — At  Lewiston  and  Asotin,  Ida.,  re- 
markably severe  hail-storms  occurred,  killing  a  large 
number  of  sheep  and  fowls,  and  birds  by  hundreds. 

June  12th,  1881. — Very  destructive  hail-storms  oc- 
curred in  Iowa,  where  farm  crops  were  ruined,  calves, 
hogs,  and  fowls  killed,  and  stock  badly  bruised.  Hail- 
stones, some  of  which  were  the  size  of  a  man' s  fist,  drift- 
ed in  places  two  or  three  feet  deep.  The  storms  were 
most  violent  in  the  counties  of  Henry,  Guthrie,  Pot- 
tawattamie,  Audubon,  and  Cass. 

June  4ih,  1882. — A  destructive  hail-storm  occurred 
east  of  Freehold,  N.  J.,  its  path  being  thirty  miles 
long  and  half  a  mile  wide. 

June  8t7i,  1882. — At  Laredo,  Tex.,  very  large  hail 
fell,  single  stones  weighing  a  pound. 

June  16th,  1882. — At  Dubuque,  la.,  hail-stones  fell 
from  one  to  seventeen  inches  in  circumference,  the 
largest  weighing  twenty-eight  ounces,  the  size  of 
lemons.  These  stones  were  of  diverse  and  peculiar 
formations,  some  evidently  being  agglomerations,  as 
they  were  covered  with  knobs  and  projections,  prob- 
ably formation  similar  to  Fig.  16,  C,  on  p.  79.  Other 
(stones  were  composed  of  alternate  ice-layers  of  vary- 


240  AMERICAN    WEATHER. 

ing  shades  of  color  and  degrees  of  transparency.  It 
was  reported  that  these  layers  had,  in  some  instances, 
gravel  and  bits  of  grass  imbedded  within  them,  but 
probably  these  foreign  substances  resulted  from  con- 
tact with  the  ground  where  they  fell. 

August  10th,  1882. — Wyoming  Co.,  N.  Y.,  a  severe 
storm  occurred,  with  a  hail  belt  four  miles  wide  and 
about  forty  miles  long,  and  stones  as  large  as  hickory- 
nuts. 

During  the  night  of  August  7th  and  8th,  1883,  a 
very  severe  hail-storm  occurred  in  Lac  and  Audubon 
counties,  la.  In  the  former  county  the  hail  was  un- 
usually large,  and  in  such  quantities  that,  in  places,  it 
was  yet  unmelted  two  days  after.  Grain  was  de- 
stroyed, small  animals  and  poultry  killed.  The  larg- 
est hail-stones  measured  thirteen  inches  in  circumfer- 
ence, near  Gray,  Audubon  Co.,  where  twenty-one  cattle 
were  killed.  The  drifted  hail  was  said  to  have  covered 
fence  tops  and  to  have  delayed  railroad  trains. 

July  8th,  1883. — Severe  hail-storms  occurred  in  David- 
son Co.,  Dak.  JN"ear  Morriston  the  hail  belt  was  two 
and  one  half  miles  wide  and  thirty  miles  long ;  near 
Huron,  two  and  one  half  miles  wide  and  about  twenty 
miles  long  ;  both  belts  extended  from  northwest  to 
southeast. 

June  7th,  1886. — In  San  Miguel  and  Lincoln  coun- 
ties, N".  M.,  hail-storms  did  great  damage,  killing  a 
number  of  sheep,  cattle,  and  horses. 

June  26th,  1886. — A  destructive  hail-storm,  with  a 
path  twenty  miles  long  and  two  miles  wide,  passed 
through  Walsh  and  Grand  Forks  counties.  Dak.,  de- 
stroying all  crops  and  leaving  so  much  hail  that  it  did 
not  all  melt  within  thirty  hours. 

July  24th,  1886. — Unusually  destructive  hail-storms 
occurred  in  Dakota  and  Minnesota,  Near  Gfraf  ton  the 


AMERICAN"   WEATHER.  241 

stones  were  as  large  as  liens'  eggs.  The  path  of  the 
storm  was  five  miles  wide  and  thirty  long.  Quarter  of 
a  million  acres  of  wheat  were  said  to  have  been  entirely 
destroyed  in  that  section  alone. 

August  10th,  1886. — During  a  storm  at  Fort  Yates, 
Dak.,  hail- stones  fell  as  large  as  three  and  one  half 
inches  in  diameter.  They  were  spherical  in  shape,  cen- 
tre composed  of  dry,  compact  snow,  outside  layer  very 
hard  ice  with  cylindrical  protuberances  projecting  from 
the  sides  from  one  half  to  three  fourths  of  an  inch. 

THUNDER-STORMS. 

It  has  been  pointed  out,  by  Dr.  Meldrum  it  is  be- 
lieved, that  essential  elements  to  thunder-storms  are 
masses  of  descending  cold  air,  along  with  other  ascend- 
ing currents  of  warm,  moist  air.  This  theory  tends  to 
explain  the  infrequency  of  lightning  storms  in  Cali- 
fornia and  Arizona,  where  the  climate  is  not  only  dry, 
but  where  the  atmospheric  disturbances  are  such  that 
descending  cold  currents  are  of  rare  occurrence. 

The  favoring  conditions  for  thunder-storms  depend 
largely  on  the  current  action  of  the  solar  heat,  as  is 
shown  by  the  fact  that  these  storms,  while  maintaining 
their  sphere  of  action  at  quite  uniform  distances  from 
the  cyclonic  centre,  die  out  at  nightfall  and  recommence 
the  next  morning. 

It  is  well  known,  in  a  general  way,  that  thunder- 
storms do  not  occur  with  the  same  frequency  through- 
out the  United  States.  As  regards  the  monthly  fre- 
quency, the  winter  months  have  the  least  and  the  sum- 
mer months  have  the  most  thunder-storms. 

Thunder-storms  are  most  frequent  in  Florida  and  the 
Mississippi  and  lower  Missouri  valleys,  the  average 
annual  number  being  from  thirty-five  to  fifty.  Over 
the  lake  region  the  number  falls  to  twenty,  and  in  Few 


242  AMERICAN   WEATHER. 

England  to  ten  annually.  To  the  westward  of  the 
Rocky  Mountains  the  annual  average  number  is  less 
than  ten  for  the  whole  region,  while  in  Southern  Cali- 
fornia one  or  two  years  may  pass  without  a  manifesta- 
tion of  thunder  or  lightning. 

Electrical  discharges  which  take  place  between  sepa- 
rate clouds,  or  between  clouds  and  earth,  follow  an  ir- 
regular path,  taking  the  route  of  the  least  electrical 
resistance  between  the  separate  objects.  Franklin's 
discoveries  a  century  ago  proved  that  these  discharges 
and  those  from  electrical  machines  are  identical  in  char- 
acter. Electrical  flashes  pass  with  such  enormous  ve- 
locity that  one  cannot  say  with  absolute  accuracy 
whence  or  to  what  point  the  discharge  travels.  It  is 
safe  to  assert  that  all  appearances  of  lightning,  whether 
distinct  flashes  or  sheet  or  heat  lightning,  are  coin- 
cident with  the  presence  of  thunder-storms,  the  only 
difference  being  that  in  case  the  flash  is  below  the  ho- 
rizon or  concealed  by  intervening  clouds,  the  spectator 
sees  the  reflection  of  or  the  illumination  caused  by  the 
electrical  discharge. 

The  phenomenon  known  as  globular  lightning,  where 
globes  of  fire  appear  and  move  very  slowly,  occasion- 
ally exploding  with  great  violence,  has  not  yet  been 
satisfactorily  explained. 

It  is  unnecessary  to  point  out  the  tremendous  force 
exerted  by  lightning,  and  its  consequent  damage 
done  in  its  passage  to  the  earth.  Death  most  fre- 
quently results  from  the  passage  of  a  flash  of  light- 
ning through  a  person,  but  there  are  exceptions  to 
this  rule. 

By  a  phenomenon  termed  return  shock,  persons  are 
said  to  be  killed  without  there  being  any  visible 
flash  between  their  bodies  and  the  electrified  cloud. 
In  this  case,  death  is  supposed  to  follow  from  the  per- 


AMERICAN  WEATHER.  243 

son  having  been  fully  charged  with  electricity  of  an 
opposite  kind  to  that  in  the  cloud,  and  when  the  dis- 
charge takes  place  the  electricity  quits  the  body  with 
such  violence  as  to  be  fatal  to  the  individual. 
!"  Dwelling-houses  and  their  contents  are  believed  to  be 
tolerably  safe  from  serious  damage  when  they  are  prop- 
erly provided  with  lightning-rods.  An  essential  point 
in  furnishing  a  building  is  that  such  rod  must  be  per- 
fectly continuous  from  its  highest  point  to  the  ground, 
and  to  insure  this  all  joints  should  be  soldered  or  welded 
carefully.  Care  must  be  taken  to  examine  the  rods 
from  year  to  year,  and  insure  that  their  conductivity  is 
not  impaired  by  rust  or  corrosion  breaking  the  rod's 
continuity.  The  rod  must  be  buried  sufficiently  deep 
in  the  earth  to  connect  with  moist  soil,  preferably  with 
water-mains,  springs,  or  drains,  and  in  being  attached 
to  the  building  should  be  connected  with  extensive 
metal  part  and  adjacent  water-pipes. 

The  question  as  to  whether  high  buildings,  tall  trees, 
and  other  prominent  features  of  the  landscape  draw 
lightning  strokes  or  not,  is  a  mooted  one.  No  doubt 
exists  that  these  prominent  objects,  being  nearer  the 
thunder-cloud,  have  consequently  greater  liability  of 
being  struck,  since  they  must  more  frequently  furnish 
paths  of  lesser  resistance  to  the  passage  of  the  light- 
ning to  the  earth  than  do  lower  objects. 

Dr.  Hellmann  shows  that  the  geological  character  of 
the  soil  has  much  to  do  with  frequency  of  lightning 
strokes,  the  proportion  being  one  for  chalk-bed,  seven 
for  clay,  nine  for  sand,  and  twenty-two  for  loam.  Oaks 
are  most  often  and  beeches  least  often  struck,  and  nearly 
always  in  the  clear  or  at  the  forest's  edge.  The  risk  of 
houses  being  struck  increases  with  segregation  and 
height,  and  is  five  times  greater  in  the  country  than  in 
the  city  districts.  In  fifteen  years'  average  the  number 


244  AMERICAN   WEATHER. 

of  people  killed  in  Prussia  was  4.4  ;  in  Baden,  3.8  ;  in 
France.  3.1  :  and  in  Sweden,  3.0. 

DUST-STORMS. 

In  very  dry  countries  during  the  rainless  season  local 
whirlwinds  occasionally  pass  over  limited  sections,  the 
disturbance  being  similar  to  that  of  a  feeble  tornado. 
Such  disturbances  occur  without  rain,  and,  in  conse- 
quence, columns  of  dust  or  fine  sand  arise.  In  the 
deserts  of  Africa,  Arabia,  and  India  these  dust-storms 
are  of  such  violence,  that  in  connection  with  the  high 
temperatures  which  often  accompany  them,  they  over- 
whelm and  occasionally  destroy  passing  travellers. 
In  the  United  States  such  conditions  at  times  prevail, 
but  never  with  any  great  violence,  in  the  sandy  deserts 
of  California  and  Arizona. 

After  prolonged  dry  spells  such  storms  occasionally 
occur  immediately  over  or  to  the  eastward  of  regions 
covered  with  scanty  vegetation. 

On  March  26th,  27th,  1880,  unusually  violent  wind 
storms  occurred  in  Nebraska,  Kansas,  Iowa,  Indian 
Territory,  Texas,  and  Missouri.  As  a  rule,  very  little 
rain  fell  during  these  storms,  so  that  the  air  was  filled 
with  dust  and  fine  sand  to  such  an  extent  that  the  sun 
was  almost  obscured.  Professor  Mpher  reported  that 
all  Missouri,  except  the  extreme  southern  part,  suffered 
from  these  phenomenal  conditions.  "  The  atmos- 
phere," he  says,  "  was  filled  during  the  whole  day 
(27th)  with  a  fine  grayish  dust,  which  in  Western  Mis- 
souri and  Eastern  Kansas  was  so  dense  as  to  obscure 
the  light  of  the  sun  and  to  render  objects  invisible  at 
a  distance  of  from  100  to  300  yards."  At  Howard, 
Neb.,  dust  gathered  in  drifts  varying  from  twelve  to 
twenty  inches  in  depth. 

The  peculiar  atmospheric  conditions  known  as  dry 


AMERICAN   WEATHER.  245 

fogs,  or  those  where  the  sun  is  partly  obscured  without 
the  intervention  of  clouds,  arise  from  dust,  smoke,  or 
other  impurities  which  have  been  undoubtedly  raised 
to  the  upper  strata  of  the  atmosphere  through  the 
action  of  cyclonic  winds,  and  which,  owing  to  their 
minuteness  and  small  weight,  remain  for  days  or  weeks 
in  the  atmosphere,  upborne  by  continuing  currents. 

The  haze  peculiar  to  the  season  known  as  Indian 
summer  is  simply  a  dry  fog,  where  the  impurities  in 
the  atmosphere  remain  a  long  time,  owing  to  the  ab- 
sence of  rain.  The  greater  part  of  the  impurities  are 
smoke  from  prairie  or  forest  fires.  The  most  remark- 
able condition  of  dry  fog  in  the  United  States  was  that 
which  was  experienced  between  September  1st  and 
10th,  1Q31,  between  meridians  67  and  87  W.  and  the 
40th  arM  45th  parallels.  Prairie  and  forest  fires  had 
raged  with  very  destructive  violence  throughout  north- 
ern Michigan  and  portions  of  Canada,  from  which  this 
smoke  drifted  slowly  eastward.  The  intensity  of  these 
conditions  was  the  greatest  on  September  6th,  at  which 
time,  over  the  Atlantic  States,  from  New  Hampshire 
southward  to  North  Carolina,  the  sun  was  very  largely 
or  entirely  obscured  by  the  haze  in  the  atmosphere.  In 
Connecticut,  Massachusetts,  Rhode  Island,  and  Ver- 
mont the  absence  of  light  was  such  that  business  was 
largely  interfered  with,  and  artificial  light,  even  at 
midday,  was  rendered  necessary  in  public  and  private 
places  of  business.  Many  people  were  much  alarmed 
by  the  peculiar  atmospheric  conditions.  At  Salem, 
Mass.,  the  day  was  the  most  remarkable  one  since  the 
famous  dark  day  of  May  19th,  1780. 


CHAPTER  XIX. 

DROUGHTS  AND  HEATED  TEEMS. 

IT  is  difficult  to  say  definitely  what  is  a  drought,  as 
meteorologists  have  not  agreed  upon  this  point.  It  is 
evident  that  the  absence  of  rain  for  a  single  month,  or 
its  falling  in  very  small  quantities,  does  not  necessarily 
constitute  a  drought,  since  in  certain  sections  of  the 
United  States,  such  as  California,  Nevada,  and  Ari- 
zona, certain  months  are  rainless  and  others  are  marked 
only  by  passing  showers. 

It  would  seem  advisable  that  some  method  should  be 
followed  in  describing  droughts,  and  the  author  would 
suggest  that  the  term  be  used  only  in  connection  with 
those  sections  where  the  average  rainfall  exceeds  one 
inch  in  each  month,  and  that  the  scale  of  severity 
should  increase  from  1  upward. 

From  an  examination  of  the  records  it  appears  that 
droughts  are  very  severe  whenever  the  rainfall  for  one 
or  more  months  is  less  than  fifty  per  centum  of  the 
average  amount.  It  is  suggested  that  the  drought 
unit  indicate  a  deficiency  of  rainfall  equal  to  twenty- 
five  per  centum  for  a  single  month,  the  deficiency  to 
be  determined  with  reference  to  the  average  monthly 
amount  during  the  time  in  which  the  drought  prevails. 

Under  this  scale  the  very  severe  drought  of  1887  in 
the  northwestern  part  of  the  United  States  would  be 
indicated  by  the  numbers  7  to  14,  according  to  locality 
and  rainfall  deficiencies. 

It  is  needful  to  treat  the  subject  of  droughts  together 


AMERICAN   WEATHER.  247 

with  that  of  prolonged  and  excessive  heat,  since  this 
last  condition  never  prevails  in  the  United  States  ex- 
cept as  a  result  of  deficient  precipitation,  either  over 
the  regions  in  question  or  those  immediately  to  the 
westward  or  southward  of  it. 

The  excessive  heats  of  August,  1876,  from  Maine 
southward  to  Virginia,  and  westward  to  Ohio,  were 
coincident  with  a  rainfall  varying  from  one  fourth  to 
one  half  of  the  normal  amount  for  August.  The  under- 
lying cause  of  scanty  rainfall  in  the  northern  part  of 
the  United  States  likewise  increases  the  temperature 
unduly,  by  inducing  continued  southern  winds.  This 
cause  is  the  slow  passage  of  feeble  cyclonic  storms 
across  the  United  States  in  paths  of  very  high  latitude. 
In  August,  1876,  to  the  eastward  of  the  95th  meridian, 
no  cyclonic  storm  passed  over  the  United  States  in 
latitudes  to  the  southward  of  the  45th  parallel. 

In  connection  with  the  unparalleled  heated  term  of 
July  and  August,  1881,  it  is  to  be  noted  that  in  the 
former  month  only  one  of  the  four  cyclonic  storms 
moved  eastward  in  a  path  to  the  southward  of  the  46th 
parallel,  and  in  August  no  storm  crossed  the  country 
to  the  eastward  in  a  path  to  the  southward  of  the  46th 
parallel.  Besides,  the  five  storms  of  the  latter  month 
were  all  of  very  feeble  character,  except  one  in  South- 
ern Florida. 

To  summarize  briefly,  prolonged  heated  terms  result 
(1)  from  conditions  of  summer  drought,  where  the 
parched  earth  readily  receives  heat  from  the  sun,  which 
is  radiated  to  surrounding  objects  without  any  consid- 
erable quantity  of  it  being  spent  in  transforming  into 
aqueous  vapor  the  usual  moisture  at  the  surface  of  the 
earth,  caused  by  the  average  rainfall ;  and  (2)  by  such 
distributions  of  atmospheric  pressure  as  cause,  over 
the  districts  affected,  the  prevalence  of  warmer  winds 


248  AMERICAN  WEATHER. 

from  more  southerly  latitudes  or  from  drought-stricken 
districts.  In  the  United  States  this  distribution  of 
pressure  looks  to  the  slow  passage  of  areas  of  low  press- 
ure eastward  across  the  extreme  northern  part,  thus 
inducing  from  the  Gulf  of  Mexico  to  the  northern 
boundary  southerly  or  southwesterly  winds,  which, 
being  originally  of  high  temperature,  still  retain  their 
heat  and  also  lose  their  moisture  in  passing  over  the 
drought  districts. 

During  July  and  August,  1876,  there  was  a  very 
severe  drought  from  Maine  southward  to  Virginia,  and 
westward  to  Pennsylvania  and  Michigan.  Crops  were 
seriously  damaged,  wells  and  streams  became  dry,  and 
industrial  establishments  were  closed.  From  the  early 
part  of  July  to  the  end  of  August,  over  New  England, 
New  York,  and  Pennsylvania,  the  rainfall  averaged 
only  about  an  inch,  which  is  less  than  one  fourth  of 
the  usual  amount. 

The  most  extensive,  prolonged,  and  disastrous 
drought  of  the  United  States  is  probably  that  of  July, 
August,  and  September,  1881,  which  affected  the  entire 
country  east  of  the  Mississippi  River.  During  July 
and  August  the  drought  was  also  bad  in  Kansas  and 
Arkansas.  During  August  less  than  one  eighth  of  the 
usual  amount  of  rain  fell  in  the  Ohio  Valley,  less  than 
one  third  in  the  Middle  Atlantic  States,  and  only 
about  two  fifths  in  New  England  and  the  region  along 
Lakes  Ontario  and  Erie. 

By  the  early  part  of  September  a  lamentable  condi- 
tion of  affairs  existed  to  the  eastward  of  the  Mississippi 
River  as  far  northward  as  Illinois  and  New  York. 
The  wells,  cisterns,  and  springs  that  had  never  before 
gone  dry  were  exhausted,  and  nearly  all  the  rivers  of 
the  country  were  at  the  lowest  state  ever  known. 
Pastures  were  parched  and  crops  badly  injured  or  en- 


AMERICAN  WEATHEK.  249 

tirely  destroyed.  Water  was  so  scarce  in  many  places 
that  cattle  suffered  greatly  for  want  of  it,  and  numer- 
ous manufacturing  industries  were  sadly  interfered 
with  or  entirely  discontinued.  In  McKean  and  Alle- 
ghany  counties,  N.  Y.,  one  thousand  oil-wells  shut 
down  for  lack  of  water  to  run  engines.  On  the  New 
York  Central  Railroad  freight  trains  were  seriously 
delayed  by  lack  of  water  for  steam,  and  in  scores  of 
towns  and  cities  manufacturing  industries  were  run  on 
short  time,  or  greatly  inconvenienced.  Many  cities 
were  obliged  to  draw  their  water-supply  from  new 
sources,  and  New  York  City  was  compelled  to  draw 
upon  the  upper  reservoirs  in  Putnam  Co.  and  the 
storage  reservoirs  at  Lake  Mahopac. 

In  1886  a  severe  and  prolonged  drought  prevailed  in 
Northeastern  Dakota  and  Northwestern  Minnesota.  It 
commenced  about  the  middle  of  June,  and  lasted  until 
the  end  of  October,  and  its  injurious  effects  were  sup- 
plemented by  unusually  high  temperatures.  During 
June  and  July  the  limits  of  the  drought  were  more 
extensive,  and  included  a  considerable  part  of  Nebraska 
and  Kansas,  Northern  Iowa  and  Western  Wisconsin, 
and  nearly  all  of  Minnesota.  Professor  Snow  says 
that  this  drought,  with  only  2.85  inches  of  rainfall 
from  June  26th  to  September  16th,  a  period  of  eighty- 
one  days,  was  of  the  same  duration  and  the  only  seri- 
ous one  in  the  vicinity  of  Lawrence,  Kan.,  since  that 
of  1874,  when  in  eighty  days  only  2.19  inches  of  rain 
fell. 

The  drought  of  1887  was  one  of  the  most  prolonged 
as  well  as  severe  droughts  ever  experienced  in  the 
United  States.  During  the  six  months  from  May  to 
October,  1887,  the  rainfall  was  only  from  sixty-five  to 
seventy-five  per  centum  of  the  average  over  Kentucky, 
Ohio,  Michigan,  Indiana,  Illinois,  Missouri,  Iowa,  and 


250  AMERICAN  WEATHER. 

parts  of  Wisconsin,  Minnesota,  Nebraska,  and  Dakota. 
Less  than  one  half  the  usual  rain  fell  in  these  months 
over  Central  Ohio,  along  the  Ohio  Valley  from  Louis- 
ville to  Cairo,  and  parts  of  Illinois  and  Wisconsin. 

In  the  early  year  the  drought  covered  a  much  larger 
area,  being  also  severe  over  Kansas,  Indian  Territory, 
and  Texas,  but  was  broken  in  Kansas  about  the  end  of 
April,  and  in  other  sections  during  May. 

HEATED   TERMS. 

In  occasional  summers  extensive  portions  of  the 
United  States  are  subject  to  excessive  and  dangerous 
temperatures,  which,  when  prolonged  for  several  days, 
are  known  as  heated  terms. 

In  July,  1876,  there  were  continued  high  tempera- 
tures during  the  greater  portion  of  the  month  through- 
out the  United  States  east  of  the  Rocky  Mountains, 
the  heat  in  many  places  becoming  so  intense  as  to  pro- 
duce fatal  results,  to  cause  the  suspension  of  business, 
and  to  augment  the  death-rate  of  many  of  the  large 
cities  to  the  highest  percentage.  Temperatures  of  or 
near  100°  occurred  on  several  successive  days  from 
Jacksonville  and  Montgomery  northward  to  Pittsburg 
and  New  York. 

In  July,  1878,  there  was  a  heated  term  almost  unpre- 
cedented in  its  severity,  continuance,  and  fatal  results, 
from  Missouri  and  Iowa  eastward  to  New  England  and 
the  Middle  States.  From  the  2d  to  the  5th,  inclusive, 
very  high  temperatures  prevailed  in  New  England  and 
the  vicinity  of  New  York  City,  and  in  these  sections 
over  fifty  sunstrokes  occurred,  many  of  which  were 
fatal.  From  the  12th  to  the  22d  the  country  was  free 
from  the  passage  of  any  low-area  storms,  except  slight 
depressions  along  the  northern  lakes  and  the  St.  Law- 
rence Valley,  the  result  of  which  was  to  induce  warm 


AMEKICAK  WEATHER.  251 

and  dry  southerly  winds  over  the  eastern  part  of  the 
country. 

During  this  period  the  hottest  days  of  the  year  nat- 
urally occur,  but  their  severity  was  augmented  by  the 
conditions  above  noted,  so  that  excessively  high  tem- 
peratures, both  night  and  day,  prevailed.  The  inten- 
sity of  the  heat  was  such  that  business  was  partly  sus- 
pended, and  in  ten  days  over  five  hundred  cases  of 
prostration  from  sunstroke  occurred,  a  large  portion  of 
which  were  fatal.  One  hundred  and  sixty -three  per- 
sons were  said  to  have  died  in  St.  Louis  alone  from 
sunstroke,  and  probably  throughout  the  country  300 
persons  perished  from  the  direct  effects  of  the  intense 
heat,  while  the  increased  death-rate  in  the  large  cities 
indicated  that  hundreds  of  others  died  indirectly  from 
the  prolonged  high  temperature. 

From  September  12th-15th,  1882,  a  succession  of  very 
hot  southerly  and  southwesterly  winds  was  experi- 
enced over  Kansas  and  Missouri,  during  which  temper- 
atures ranging  from  100°  to  110°  were  recorded.  Vege- 
tation was  burned  up,  and  the  air  at  times  was  filled 
with  clouds  of  suffocating  dust. 

Professor  Snow  says  :  "  During  these  simoons  (at 
Lawrence,  Kan.)  the  air  was  excessively  dry,  the  rela- 
tive humidity  sinking  to  seven  per  centum  the  after- 
noon of  the  12th.  The  fierce  dry  heat  burned  the  foli- 
age of  trees,  so  that  they  crumbled  to  powder  at  a 
touch." 

The  cause  of  these  burning  winds  is  easily  found  in 
the  fact  that  in  eastern  Colorado,  as  indicated  by  the 
observations  at  Las  Animas  and  Denver,  Col.,  no  rain 
fell  during  September,  and  at  Lawrence,  Kan.,  only 
0.10  in  over  a  month  immediately  prior  to  these  winds, 
so  that  the  country  to  the  west  and  south  was  parched 
by  fierce  droughts  and  the  burning  sun. 


252  AMERICAN  WEATHER. 

In  June,  1877,  from  the  8th  to  the  12th,  excessively 
high  temperatures  occurred  in  California,  ranging  from 
93°  at  San  Diego  to  114°  at  Yuma  and  122°  at  Spring 
Valley.  It  is  an  interesting  fact  that  during  this 
period  ice  formed  within  600  geographical  miles  of  these 
extreme  temperatures,  at  Cheyenne,  Wyo. 

In  the  Gila  Valley,  Ariz.,  over  an  area  of  thousands 
of  square  miles,  the  monthly  mean  temperature  of  the 
month  was  from  93°  to  94°.  At  Fort  Yuma  the  daily 
maximum  temperature  did  not  sink  any  day  below 
103°,  and  the  mean  was  110°  for  the  month.  For 
eleven  consecutive  days  the  lowest  temperature  was 
never  below  77°,  while  the  highest  day  temperatures 
ranged  from  106°  to  118°. 

One  of  the  most  remarkable  of  these  prolonged 
periods  of  high  temperatures  in  the  United  States  was 
from  July  to  September,  1881.  During  July  there  was 
a  prolonged  heated  term  in  the  Ohio  and  Central  Mis- 
sissippi valleys.  The  temperature  reached  or  exceeded 
100°  for  several  successive  days,  and  hundreds  per- 
ished, directly  or  indirectly,  from  the  heat.  During 
these  days  the  sufferings  of  the  inhabitants  of  the  cities 
of  these  sections  were  beyond  description.  In  Cincin- 
nati two  hundred  and  thirteen  died  of  sunstroke  that 
week,  at  St.  Louis,  thirty,  and  at  Dayton,  O.,  thirty. 
In  August  the  continued  great  heat  was  yet  further 
augmented  between  the  5th  and  the  13th,  from  Missouri 
and  Iowa  eastward  to  New  England,  but  fortunately 
was  not  attended  with  fatalities  to  the  same  extent  as  in 
July.  In  September  the  rainfall  was  larger  than  usual 
in  the  Mississippi  Valley,  so  that  the  area  of  excessive 
heat  was  translated  considerably  to  the  eastward,  the 
greatest  heat  occurring  in  New  England,  New  York, 
New  Jersey,  and  Pennsylvania. 

The  immediate  Pacific  coast  region  is  noted  for  its 


AMERICAN   WEATHEK.  253 

cool,  equable  summer  temperatures,  but  in  several 
instances  the  desert  wind  of  California  has  seriously 
affected  the  immediate  coast.  The  most  remarkable 
case,  that  of  June  17th,  1859,  was  at  that  time  said  to 
be  the  most  wonderful  visitation  of  this  character  in 
the  Pacific  coast  region  for  thirty  years.  At  San 
Francisco  on  that  date  the  thermometer  is  said  to  have 
registered  a  rise  in  the  temperature  from  77°  to  133°, 
with  a  burning  northwest  wind,  which  fortunately 
lasted  for  a  few  hours  only,  the  thermometer  register- 
ing 77°  at  7  P.M.  At  Santa  Barbara,  on  the  same  day 
(in  the  afternoon),  a  strong  easterly  wind  set  in,  during 
which  the  burning  air  was  filled  with  dense  clouds  of 
fine  dust,  which  caused  intense  suffering,  and  drove 
every  one  to  the  nearest  shelter.  The  fruit  was  all  de- 
stroyed, and  although  the  burning  blast  lasted  but  a 
few  hours,  yet  animals,  such  as  calves,  rabbits,  and 
birds,  died  from  the  effects.  The  temperature  was  said 
to  have  reached  133°  at  Santa  Barbara,  102°  at  San 
Diego,  and  117°  at  Fort  Yuma. 

It  seems  possible  that  the  frequency  and  intensity 
of  such  visitations  have  diminished  on  the  Pacific 
coast,  since  Tennant's  record  of  hot  days  (classing  as 
such  those  on  which  the  temperature  rose  to  80°  or 
above  at  San  Francisco)  indicates  that  their  annual 
number  have  very  materially  diminished  since  1859. 
For  seven  years  prior  to  1859  such  days  averaged  thir- 
teen yearly,  and  since  that  time,  up  to  1871,  the  aver- 
age yearly  number  is  but  four.  The  immense  quantity 
of  land  placed  under  irrigation  and  the  vast  increase 
in  vegetation  are  obvious  reasons  why  there  should  be 
some  diminution  in  this  respect. 

The  provoking  cause  of  desert  winds  must  be  the 
passage  of  a  low-area  storm  parallel  with  and  a  short 
distance  off  the  Pacific  coast,  thus  causing  a  draught 


254  AMEKICAN   WEATHEE. 

of  desert  air  to  the  westward.  It  is  more  than  prob- 
able that  the  temperatures  enumerated  above  may  be 
somewhat  in  excess,  partly  owing  to  possible  error  of 
the  thermometer  and  partly  through  their  imperfect 
exposure.  There  is  no  doubt,  however,  but  some  of 
the  highest  temperatures  in  the  world  must  obtain  on 
Mojave  and  Colorado  deserts,  so  that  in  summer  any 
strong  easterly  wind  from  these  sections  must  during 
its  prevalence  raise  enormously  the  temperature  at 
coast  stations. 

The  fatal  effects  of  these  heated  terms  are  not  shown 
alone  by  deaths  through  sunstroke,  but  more  emphati- 
cally, if  less  obviously,  by  the  increased  percentages  of 
death-rates  from  all  causes.  It  has  been  stated  that  in 
July,  1876,  the  death-rate  of  many  cities  of  the  United 
States  reached  very  high  percentages,  but  even  then 
they  do  not  attain  to  the  excessive  mortality  of  some 
other  countries,  under  similar  conditions. 

In  Lower  Egypt,  a  severe  and  prolonged  heated  term 
prevailed  from  June  15th  to  July  25th,  1888,  during 
which  the  weekly  mortality  at  Cairo  increased  from  a 
little  above  forty  to  ninety-seven  and  two  tenths,  and 
in  one  quarter  to  126  per  1000. 

This  illustrates  the  importance  of  preserving  such 
natural  conditions  as  will  render  heated  terms  difficult 
and  serve  to  modify  their  existing  conditions  ;  and  in 
no  way  can  this  be  better  done  than  by  the  cultivation 
and  conservation  of  growing  vegetation,  especially  of 
woodland  and  forest,  whose  action  in  this  direction  is 
mentioned  on  page  156. 


CHAPTER  XX. 

MISCELLANEOUS   PHENOMENA. 

THERE  are  a  number  of  phenomena  and  physical  con- 
ditions, connected  more  or  less  with  climatology  and 
meteorology,  which  are  very  interesting  and  important 
in  themselves,  but  cannot  be  more  than  alluded  to. 

SEA  TEMPERATURES. 

Perhaps  the  temperature  of  the  surface  water  of  the 
sea  possesses  the  greatest  interest  and  importance  of 
the  miscellaneous  phenomena.  Its  effects  have  been 
briefly  alluded  to  in  the  chapter  on  the  distribution  of 
temperature. 

The  diurnal  range  of  surface  sea  temperatures  is 
small,  the  minimum  occurring  about  sunrise  and  the 
maximum  near  noon. 

The  temperature  of  the  surface  of  the  ocean  has  been 
observed  at  2  P.M.  daily  for  many  years  along  the 
Atlantic  coast.  The  difference  between  the  highest 
and  lowest  average  monthly  temperatures  amounts  to 
29°  at  Portland,  Me.,  and  Jacksonville,  Fla.,  from  which 
places  it  increases  to  the  southward  and  northward,  re- 
spectively, to  42°  at  Chincoteague,  Ya.  The  ranges  at 
Key  West  and  Eastport  are  nearly  identical,  being  16° 
and  18°  respectively,  while  the  average  difference  be- 
tween the  months  in  the  Gulf  of  Mexico  is  about  30°. 

The  maximum  monthly  temperature  occurs  in  the 
Gulf  of  Mexico  and  from  Key  West  northward  to  Chin- 
coteague in  July,  and  the  mean  gradually  diminishes 


256  AMERICAN  WEATHER. 

between  the  two  stations  named  from  87.4°,  at  the 
southern,  to  80°,  at  the  northern.  From  Cape  May  to 
Portland  the  maximum  average  prevails  during  August, 
and  falls  to  61°  at  the  last-named  station,  while  at 
Eastport  the  highest  temperature  is  but  50.6°  in  Sep- 
tember. The  lowest  average  temperatures  occur  in 
January  as  far  northward  as  Atlantic  City,  and  thence 
to  Portland  in  February.  As  exceptions,  Key  West 
has  the  lowest  temperature,  71.2°,  during  December, 
and  Eastport,  32.7°,  during  March. 

EARTH  TEMPERATURES. 

The  temperature  of  the  earth  is  not  generally  consid- 
ered as  of  great  iheteorological  importance,  but  obser- 
vations regarding  the  temperature  of  surface  soils,  in 
which  the  staple  crops  of  the  country  grow,  would  be 
theoretically  valuable  to  the  agriculturist. 

The  earth  is  a  bad  conductor  of  heat,  so  that  at  a  con- 
siderable depth,  say  twenty  feet,  its  maximum  temper- 
ature occurs  not  far  from  December,  and  its  minimum 
near  June,  the  dates  varying  according  to  soil  and  lati- 
tude. At  a  certain  point,  dependent  on  the  annual 
mean  temperature  and  the  character  of  the  soil,  the 
effect  of  the  sun's  heat  disappears,  and  the  influence 
of  heat  from  the  interior  of  the  earth  is  felt.  The  in- 
crease of  temperature  has  been  variously  placed  from 
1.4°  to  two  degrees  for  each  hundred  feet  of  descent. 

At  Point  Barrow,  Alaska,  the  temperature  of  the 
earth,  at  a  depth  of  thirty-seven  feet  below  the  surface, 
remained  for  months  constant  at  12°  Fahr.  Assuming 
an  increase  of  temperature  equal  to  one  degree  in  about 
fifty  feet — a  low  estimate — the  earth  is  there  frozen  to  a 
depth  of  over  one  thousand  feet.  At  Jakutsk,  Siberia, 
the  earth  was  found  frozen  at  a  depth  of  382  feet, 


AMERICAN    WEATHER.  257 

It  is  probable  that  in  the  northern  parts  of  Minne- 
sota, Dakota,  and  Montana  frost  occasionally  pene- 
trates in  very  severe  winters  to  a  depth  of  seven  or 
eight  feet,  since  at  Binscarth,  Manitoba,  50°  40'  N., 
101°  W.,  frost  has  been  found  at  nine  feet. 

ATMOSPHERIC   ELECTRICITY. 

Atmospheric  electricity,  so  closely  connected  with 
thunder-storms,  deserves  and  is  receiving  attention 
from  scientists  of  high  standing.  It  has  been  satis- 
factorily established  that  rapid  changes  in  electrical 
potential  take  place  in  advance  of  and  during  the  prog- 
ress of  rain  and  thunder  storms,  but  up  to  this  time  no 
definite  march  of  electrical  phenomenon  has  been  out- 
lined as  having  an  important  bearing  on  weather  or 
weather  forecasting. 

OZONE. 

Similarly,  that  allotropic  condition  of  oxygen  known 
as  ozone  has  excited  great  interest,  owing  to  its  im- 
portant bearing  on  health,  through  its  rapid  powers  of 
oxidation  facilitating  decomposition  of  organic  sub- 
stances. No  satisfactory  or  standard  method  of  mak- 
ing ozone  observations  has  yet  been  adopted,  so  that 
the  few  observations  made  are  impaired  in  value,  as 
they  are  not  at  all  comparable. 

OPTICAL   PHENOMENA. 

There  are  various  optical  phenomena  constantly  re- 
curring in  the  atmosphere  which  give  pleasure  to  the 
spectator  by  their  wealth  and  variety  of  color,  but  do 
not  have  any  very  important  bearing  on  meteorology. 

The  glowing  color  of  the  western  sky  at  sunset, 
through  our  fine  American  weather  almost  of  daily 
occurrence,  is  the  local  sign  for  the  weather  of  the 
coming  morn  which  is  most  regarded  and  relied  on. 


258  AMERICAN  WEATHER. 

A  sunset  marked  by  beautiful  and  slowly  fading 
colors,  from  white  lights  through  orange  to  the  reds, 
as  its  final  accompaniment,  is  considered  to  presage 
that  the  coming  day  will  be  fair.  This  belief  is  veri- 
fied to  a  great  extent,  since  such  weather  occurs  in  three 
fourths  of  the  cases,  but  no  final  and  scientific  reason 
has  been  assigned  therefor,  and  the  subject  is  of  so  com- 
plicated a  character  that  it  is  not  fully  understood. 

It  has  been  pointed  out  that  when  the  sun  is  very 
low  in  the  heavens,  its  rays  traverse  a  much  longer  path 
through  the  atmosphere  to  reach  an  observer  than 
when  the  angle  of  inclination  is  greater.  The  air  dis- 
perses the  rays  of  light  somewhat  as  does  a  prism, 
and,  as  is  known,  the  aqueous  vapor  and  air  strata,  of 
varying  quantities  and  densities,  change  the  sky  colors 
at 'sunset  through  various  processes,  such  as  absorp- 
tion, diffraction,  refraction,  interference,  and  reflection. 
When  the  atmosphere  is  quite  free  from  violent  dis- 
turbances, and  the  aqueous  vapor  is  not  only  present  in 
quantities  below  the  average,  but  is  also  quite  regularly 
distributed,  its  reduced  quantity  and  comparative  homo- 
geneity permit  the  various  optical  processes  of  the  solar 
rays  to  proceed  slowly,  regularly,  and  gradually,  until 
they  end  in  the  red  glows.  When  conditions  of  violent 
disturbance,  such  as  precede  storms,  obtain  in  the 
upper  atmosphere,  it  is  reasonable  to  assume  that  such 
varying  conditions  of  air  density  and  vapor  must  cause 
the  modifying  process  to  proceed  irregularly  to  such  an 
extent  as  to  produce  at  sunset  the  cold,  harsh  contrasts 
of  cloud  color  which  are  viewed  as  preceding  rain. 

Scott  has  pointed  out  that  a  knowledge  of  these  con- 
ditions is  of  value,  largely  owing  to  the  fact  that  the 
march  of  weather  phenomena  is  from  west  to  east  in  the 
Northern  Hemisphere. 

Rainbows  have  no  meteorological  significance,  being 


AMERICAN  WEATHER.  259 

produced  simply  by  reflection  and  refraction  from  drops 
of  water,  and  may  be  seen  in  the  spray  of  fountains  or 
waterfalls.  Fogbows  and  lunar  rainbows  are  similar 
phenomena,  but  of  rarer  occurrence. 

The  observer  of  a  rainbow  well  knows  that  he  is 
always  situated  exactly  on  a  line  between  the  sun  and 
the  bow  itself,  which  line,  if  extended  from  the  sun 
through  the  observer's  eye,  would  end  in  the  very 
centre  of  a  circular  rainbow.  There  may  be  two  bows — 
the  primary,  with  the  red  outside,  and  the  secondary, 
with  the  red  inside.  Inside  the  primary  bow  or  out- 
side the  secondary  bow  may  be  other  supernumerary 
bows  of  red  and  green  alternately. 

Halos  are  circles  of  prismatic  colors  around  the  sun 
or  moon,  and  generally  have  radii  of  22°  or  45°,  while 
coronas  are  faintly  colored  concentric  circles  of  very 
small  diameter,  with  radii  from  4°  to  8°,  immediately 
around  the  moon.  Coronas  have  the  blue  color  nearest 
the  moon,  while  halos  have  the  red  color  nearest.  Co- 
ronas arise  from  the  passage  of  light  cirrus  clouds  or 
aqueous  vapor,  otherwise  invisible,  before  the  moon, 
thus  interfering  with  the  rays  of  light  as  they  pass  by 
the  vapor  drops.  Halos  are  formed  by  the  refraction 
and  the  reflections  of  the  solar  rays  from  ice  crystals  of 
cirrus  clouds,  or  from  ice  particles  suspended  in  the  air. 

In  the  author's  experience  in  the  arctic  regions,  at 
Fort  Conger,  Grinnell  Land,  solar  halos  of  great  beauty 
and  remarkable  brilliancy  were  frequently  observed 
during  the  very  cold,  clear  days  of  early  spring.  In 
such  cases  double  halos,  with  four,  five,  or  six  mock 
suns  of  great  splendor,  were  not  infrequent.  In  these 
cases  refraction  and  reflection  of  the  sun's  rays 
were  from  minute  spiculse  of  ice,  which,  suspended 
in  the  air,  were  commonly  known  to  the  men  of 
the  expeditionary  party  as  "  frost  in  the  air,"  At 


260  AMERICAN   WEATHER. 

times  the  solar  halos  and  mock  suns  were  visible 
against  a  background  of  a  high  hill  less  than  a  mile 
distant. 

These  halos  by  observation  formed  exactly  under 
conditions  when,  according  to  Scott,  "  they  would  be 
theoretically  producible  if  the  rays  were  refracted 
through  minute  crystals  of  ice  floating  in  the  air  in  all 
sorts  of  positions." 


FIG.  32.— LUNAR  HALO  AT  FORT  CONGER,  FEB.  1,  1882. 

On  February  1st,  1882,  at  Fort  Conger,  the  author 
saw  a  most  remarkable  lunar  halo,  of  which  an  imper- 
fect idea  is  given  by  Fig.  32,  when  the  moon  was 
about  25°  above  the  horizon.  The  circles  of  22°  and 
46°  were  perfect  to  the  horizon,  and  were  both  tipped 
with  contact  arches.  Six  mock  moons  were  present 


AMERICAN   WEATHER.  261 

— two  on  either  side  of  the  true  moon  and  two  above 
it — all  of  which  showed  brilliant  prismatic  colors, 
very  like  the  clear,  distinct  colors  seen  in  rainbows. 
Spears  of  light  extended  from  the  moon  vertically, 
reaching  downward  to  the  horizon  and  upward  to  the 
outer  circle.  In  addition,  a  narrow  streak  of  clear, 
white  light  extended  from  the  moon  horizontally  on 
both  sides  completely  around  the  entire  horizon,  at  an 
altitude  of  25°,  the  same  as  that  of  the  moon  itself. 
At  times  G,  faint  mock  moon  without  rainbow  colors 
was  to  be  seen  at  90°  distant  from  the  moon,  being  in 
the  north,  while  the  moon  itself  was  in  the  east,  and  a 
second  faint  one  under  the  moon,  so  that  eight  mock 
moons  were  visible  at  one  time.  The  halo  lasted  an 
hour,  the  number  of  moons  varying  during  that 
time. 

Halos  are  supposed  to  indicate  coming  rain  or  snow, 
and  Professor  Laughlin,  a  voluntary  observer  in  Ten- 
nessee, reports  that  from  observations  taken  during  1884 
and  1885,  eighty-six  per  centum  of  halos  observed  and 
ninety-three  per  centum  of  coronas  were  followed  by 
precipitation  within  three  days. 

Probably  the  most  remarkable  series  of  solar  halos 
seen  in  the  United  States  were  those  from  December 
29th- 31st,  1880,  in  the  Ohio,  upper  Mississippi,  and 
lower  Missouri  valleys.  At  that  time  the  temperature 
of  these  sections  was  below  zero,  Fahrenheit.  The 
halos  were  frequently  double,  being  of  22°  and  46°  radii, 
with  brilliant  contact  arches.  Generally  the  prismatic 
colors  showed  with  great  distinctness,  and  mock  suns, 
varying  in  number  from  two  to  five,  were  frequent. 

The  images  of  the  sun — often  showing  prismatic  colors 
— at  the  intersecting  points  of  the  circle  are  called  par- 
helia, or  mock  suns,  and  those  of  the  moon  paraselence, 
or  mock  moons. 


262  AMEKICAN  WEATHEK. 

Glories,  called  anihelia,  are  sometimes  seen  to  sur- 
round the  shadow  of  an  observer's  head  when  cast  on 
fog  or  cloud. 

A  most  remarkable  optical  phenomenon  was  observed 
by  the  author  on  May  3d,  1882,  opposite  Henrietta 
Nesmith  Glacier,  Grinnell  Land.  A  beautiful  mock 
sun,  accompanied  by  clearly  defined  prismatic  colors, 
was  seen  against  the  only  light  clouds  in  the  heavens, 
at  a  distance  of  about  120°  from  the  sun. 

Flammarion  says  of  this  rare  and  remarkable  phe- 
nomenon :  ' f  Sometimes  the  solar  rays  experience  two 
successive  reflections  upon  the  vertical  surfaces  of  one 
of  the  prisms.  There  is  then  visible,  at  120°  from  the 
sun,  a  white  image  more  or  less  diffuse,  which  has  re- 
ceived the  name  of  parantlielion.  The  horizontal  bars 
of  the  ice  crystals  reflect  also  the  solar  light,  but  in  an 
upward  direction,  which  prevents  the  spectator  from 
perceiving  it  unless  he  be  on  the  summit  of  a  steep 
mountain  or  in  the  car  of  a  balloon,  above  the  cloud 
containing  the  icy  particles.  It  will  be  readily  ad- 
mitted that  these  conditions  can  rarely  be  fulfilled  ; 
but  MM.  Barral  and  Bixio  were  fortunately  able  to 
realize  them  on  July  27th,  1850.  The  image  of  the  sun 
thus  reflected  appears  almost  as  luminous  as  the  sun. 
Bravais  suggested  for  this  phenomenon,  at  once  so  re- 
markable and  so  rare,  the  name  of  pseudolielion" 

Mirage  is  an  image  produced  by  the  successive  bend- 
ing of  rays  of  light  in  passing  through  the  strata  of  air 
of  varying  densities.  It  is  particularly  frequent  over 
dry,  sandy  wastes,  and  in  the  United  States  is  not  un- 
common in  the  southwestern  States  and  Territories. 
It  is  likewise  common  in  the  polar  regions,  especially 
across  the  open  water  to  heavy  ice  or  land.  Remark- 
able stories,  which  the  author,  from  his  experience  on 
land  and  sea,  can  well  credit,  have  been  told  of  trav- 


AMERICAN   WEATHER.  263 

ellers  being  led  to  believe  these  airy  phantoms  to  be 
living  lakes,  extensive  forests,  and  great  cities. 

AURORA   BOREALIS. 

The  weird  beauty  and  splendor  of  the  aurora  has 
always  engaged  the  attention  of  mankind,  awakening 
feelings  of  terror,  awe,  or  admiration,  according  to  the 
various  views  held  by  the  populace  regarding  its  cause 
and  significance. 

Until  late  years  auroras  have  been  considered  as 
meteorological  phenomena,  but  at  the  present  time 
their  active  connection  with  weather  changes  is  very 
problematical.  While  the  auroral  display  is  evidently 
a  visible  manifestation  of  the  atmospheric  electricity, 
yet  in  view  of  its  limited  range  its  appearance  or  non- 
appearance  cannot  be  considered  as  having  more  than 
a  local  and  transient  meteorological  interest. 

The  aurora  is  never  seen  in  very  low  latitudes,  rarely 
south  of  the  fortieth  parallel,  and  only  infrequently  to 
the  northward  of  the  80°  1ST.  latitude.  The  aurora  may 
be  visible  in  the  heavens  either  to  the  south  or  north, 
according  to  the  locality  of  the  observer,  since  the  belt 
of  its  greatest  frequency  skirts  Northern  Asia,  touches 
Southern  Greenland,  and  crosses  North  America  from 
Labrador  to  Behring  Strait.  This  belt  of  frequency  is 
substantially  the  portion  of  the  northern  hemisphere 
over  which  the  greatest  atmospheric  disturbances  and 
movements  take  place,  and  attempts,  as  yet  unsuccess- 
ful, have  been  made  to  definitely  determine  that  an 
intimate  relation  exists  between  such  changes  and  these 
electrical  phenomena. 

A  fuller  treatment  of  the  subject  of  auroras  pertains 
rather  to  the  phenomena  of  terrestrial  magnetism  than 
to  meteorology. 


CHAPTEE  XXI. 

WEATHER   PREDICTIONS. 

A  BRIEF  allusion  to  the  methods  of  weather  predic- 
tions may  be  of  some  interest  to  the  general  reader. 
So  firmly  and  widely  rooted  is  the  belief  in  the  prac- 
ticability of  weather  forecasting,  that  separate  bureaus 
for  this  purpose  have  been  formed  and  are  maintained 
at  public  expense  in  the  United  States,  Great  Britain, 
France,  Germany,  Italy,  Russia,  Algeria,  Australia, 
India,  and  Japan.  Other  nations,  such  as  Sweden, 
Holland,  and  Switzerland,  co-operate  with  and  share 
the  expenses  and  benefits  of  other  larger  countries. 

The  weather  predictions  made  when  the  United  States 
weather  bureau  was  established,  in  1870,  were  exceed- 
ingly vague  and  indefinite  in  their  character,  but  in 
late  years  a  marked  change  has  been  made  in  the 
methods  followed  and  the  clearness  of  predictions 
made.  That  which  fifteen  or  twenty  years  ago  seemed 
impossible  or  wonderful  has  become  an  every-day 
occurrence,  and  with  the  increasing  knowledge  of 
meteorology  there  has  been  a  growing  demand  for  ab- 
solute accuracy  and  definiteness. 

All  skilled  meteorologists  realize  how  comparatively 
local  are  weather  conditions  and  how  impossible  it  is 
at  times  to  make  predictions  for  a  definite  period  with 
any  feeling  of  certainty.  Indeed,  weather  conditions 
vary  so  much  that  occasionally  even  the  most  skilled 
forecaster  cannot  say  with  absolute  confidence  what 
will  be  the  coming  weather  for  certain  localities,  even 


AMERICAN  WEATHEB.  265 

for  a  period  of  eight  hours  ;  while,  again,  the  condi- 
tions are  so  definite  and  clear  that  one  can  foretell  with 
a  fair  degree  of  confidence  the  weather  for  entire  dis- 
tricts and  for  periods  of  even  forty-eight  or  seventy- 
two  hours  in  advance. 

The  forecaster,  then,  has  to  bear  in  mind  that  weather 
conditions  are  largely  local,  and  so  he  must  study  with 
such  fact  prominently  in  view.  Indeed,  so  local  is  the 
weather  of  many  States  of  the  Union,  that  one  cannot 
even  attain  for  any  prolonged  period  a  higher  percent- 
age of  accuracy  than  ninety  in  describing  briefly  the 
weather  changes  of  the  past  twenty-four  hours.  The 
accuracy  of  this  statement  may  be  illustrated  by  the  fact 
that  in  1886  predictions  of  rain,  if  made  with  absolute 
correctness  for  Western  Pennsylvania,  based  on  Pitts- 
burg,  would  have  been  ten  per  centum  in  error  for  Erie, 
Pa.  In  like  manner  the  records  show  that  rain  fell  in 
Eastern  Iowa  on  twelve  per  centum  more  days  at  Du- 
buque  than  at  Davenport ;  in  Tennessee,  sixteen  per  cen- 
tum more  at  Knoxville  than  at  Nashville  ;  in  Eastern 
Michigan,  nineteen  per  centum  more  at  Alpena  than  at 
Port  Huron,  and  in  Northern  Georgia  the  difference 
amounts  to  twenty-one  per  centum  between  Atlanta 
and  Augusta.  The  forecaster,  then,  even  for  districts 
of  moderate  size,  cannot  expect  that  predictions  of  rain 
will  be  equally  successful  in  all  portions  of  the  section 
predicted  for.  It  is  evident  that  fair-weather  condi- 
tions are  those  which  are  most  persistent  and  from  the 
prediction  of  which  the  highest  percentages  of  accuracy 
will  be  obtained.  But  if  more  difficult  of  verification, 
yet  rain  predictions  are  more  important  to  the  public, 
and  so  should  be  made  more  freely  than  the  reverse. 

The  skill  of  a  weather  predictor  arises  largely  from 
his  alert  comprehensiveness  of  mind,  accurate  and  re- 
tentive memory,  phlegmatic  but  confident  tempera- 


266  AMERICAN   WEATHER. 

ment,  and  long  experience  in  connection  with  the  dis- 
cussion of  storms  for  the  section  of  the  globe  and  the 
period  of  the  year  for  which  he  predicts.  The  first  of 
these  qualities  enables  him  to  instantly  grasp  the  situ- 
ation and  promptly  draw  correct  general  inferences 
from  slight  indications,  as  does  the  skilled  physician 
in  diagnosing  obscure  cases  ;  the  second  renders  it  pos- 
sible for  him  to  recall,  with  their  sequence,  similar 
weather  conditions — a  very  important  matter — when 
they  are  typical ;  the  third  enables  him  to  maintain 
unimpaired  his  confidence  in  his  own  ability  and  judg- 
ment when  he  has  made  a  series  of  unsuccessful  predic- 
tions. Experience,  the  last  but  not  the  least,  is  most 
necessary,  since  the  attendant  circumstances  of  storms 
change  so  materially,  even  from  one  season  of  the  year 
to  another,  that  a  forecaster  skilled  in  summer  storms 
may  fail  at  first  in  discussing  those  of  the  winter.  To 
these  qualities  may  be  added  the  necessity  of  an  imag- 
inative or  creative  faculty,  since  the  configuration  and 
physical  outlines  of  a  country  have  such  important 
bearings  upon  the  development,  progress,  and  move- 
ment of  storms  as  to  render  it  essential  that  the  pre- 
dictor shall  have  the  country,  as  it  were,  actually  before 
his  eye,  instead  of  the  flat  map  on  which  the  data  is 
charted. 

The  official  may  know  and  predict  accurately  the 
general  direction  in  which  a  storm  will  move,  and  yet 
in  thickly  populated  countries,  such  as  the  northeast- 
ern part  of  the  United  States,  the  passage  of  a  storm 
only  twenty  miles  to  the  northward  or  southward  of 
the  point  fixed  in  advance  by  the  forecaster  will  result 
in  weather  conditions  which  must  disappoint  hun- 
dreds of  thousands  of  people  who  are  interested  in 
them.  This  narrow  difference  of  a  few  miles  in  pre- 
dicting twenty -four  hours  in  advance  the  path  of  a 


AMERICAN  WEATHER.  267 

storm  which  travels  600  or  700  miles  daily  is  almost 
infinitesimal  as  regards  the  storm  path  itself,  and  yet  it 
is  sufficient  to  produce  cold,  northerly  winds,  with 
snow,  in  place  of  warm,  southerly  winds,  with  rain, 
or  vice  versa. 

A  few  general  rules  for  weather  predictions  in  the 
United  States,  based  largely  on  the  author's  personal 
labors  in  forecasting,  may  be  interesting,  as  supple- 
mentary to  general  statements  made  in  previous  pages, 
and  as  of  practical  value  when  considering  doubtful  and 
uncertain  weather  conditions. 

1.  In  case  of  doubt,  and  when  the  temperature  is  ab- 
normally high  or  low,  it  is  safest  to  assume  that  the 
temperature  will  tend  to  return  to  its  normal  and 
seasonal  condition. 

2.  When  the  winds  along  the  Gulf  coast  or  Atlantic 
seaboard  have  blown  from  the  ocean  for  twenty-four 
hours,  even  if  the  cloud  formations  are  not  large,  rain 
may  be  assumed,  with  considerable  accuracy,  to  follow 
within  the  ensuing  day. 

3.  Whenever  the  United  States  is  covered  with  a 
barometric  pressure  below  the  normal,  and  no  sharply- 
defined  storm  centre  is  present,  the  chances   predomi- 
nate that  existing  weather  conditions  will  drift  slowly, 
and  with  slight  changes,  from  the  Mississippi  Valley 
to  the  Atlantic  coast. 

4.  Whenever  in  uncertain  conditions  the  barometer 
rises  in  the  southwestern  part  of  the  United  States,  the 
weather  to  the  north  and  east  will  soon  clear,  without 
there  are  decided  and  obvious  reasons  to  the  contrary. 

5.  Cyclonic  storms  which  enter  the  United  States  to 
the  westward  of  the  Mississippi  Eiver  rarely  recurve 
to  the  eastward,  but  may  be  expected  to  pass  inland 
and  die  out  within  the  confines  of  the  continent. 

6.  Cyclonic  storms,  with  paths  entirely  or  largely  in 


AMERICAN   WEATHER.  269 

orological  conditions.  Of  this  character  are  Charts 
XXII.  and  XXIII.,  which  show,  respectively,  the  aver- 
age date  of  the  last  killing  frost  and  of  the  first  killing 
frost  in  the  United  States. 

Table  No.  9  shows  how  large  a  proportion  of  the  frosts 
at  varying  stations  have  occurred  within  ten  days  of  the 
average  date,  so  that  the  value  of  this  class  of  data  may 
be  easily  determined  by  the  reader. 

In  like  manner,  Charts  Nos.  IX.  and  X.  may  be  used 
in  determining  the  probable  chances  of  such  crops  ma- 
turing as  are  dependent  on  continued  daily  mean  tem- 
peratures above  32°  and  50°  Fahrenheit. 

In  connection  with  these  charts,  the  agriculturist  or 
other  persons  interested  should  use  their  own  knowledge 
of  local  meteorology  to  supplement  these  data. 

It  may  be  well  to  here  add  a  simple  and  definite 
method  by  which  in  clear,  cool  weather,  near  the  period 
of  early  or  late  frosts,  a  person  interested  may  deter- 
mine, with  a  very  considerable  degree  of  accuracy,  if 
frost  will  occur  the  following  night. 

The  approach  of  local  frost  can  be  foretold  with  very 
considerable  accuracy  from  the  readings  of  properly 
exposed  dry  and  wet  thermometers.  A  safe  and  simple 
rule  to  follow  when  the  temperature  is  at  50°  or  below 
is  to  multiply  the  difference  between  the  readings  of 
the  thermometers  by  2.5,  and  when  the  sum  thus  ob- 
tained is  subtracted  from  the  reading  of  the  dry  ther- 
mometer, it  leaves  the  approximate  degrees  to  which 
the  temperature  of  the  air  will  fall  the  coming  night, 
unless  change  of  wind  to  a  moister  quarter  or  increase 
of  cloudiness  interferes.  The  value  and  importance  of 
observations  of  this  kind  have  not  been  sufficiently 
impressed  upon  farmers  cultivating  crops  of  a  kind 
susceptible  to  frost  and  capable  of  protection.  This 
subject  has  been  erroneously  viewed  by  many  as  too 


270  AMERICAN  WEATHER. 

abstruse  and  complex  for  practical  application  by  un- 
scientific persons.  Since  this  lowering  of  temperature 
is  caused  by  radiation,  it  follows  that  any  method 
which  will  prevent  free  radiation  must  materially 
check  the  formation  of  frost,  so  that  even  thin  cloth, 
layers  of  straw,  or  even  a  cloud  of  smoke  will  protect 
tender  plants,  unless  the  frost  is  very  severe. 

The  question  is  often  broached  as  to  whether  weather 
conditions  for  the  coming  month  or  season  can  be  fore- 
told. There  is  evidently  a  general  and  widespread  in- 
terest in  this  question,  since  on  the  desire  for  and  belief 
in  such  long-range  predictions  has  rested  the  ephem- 
eral notoriety  of  many  weather  prophets.  It  is  a  gen- 
eral scientific  admission  that  as  yet  the  advances  of 
meteorology  are  insufficient  to  justify  predictions  of 
the  weather  for  a  season  in  advance.  There  are  appar- 
ently good  grounds  for  believing  that  general  laws  can 
be  deduced  by  which  for  certain  parts  of  the  globe  it- 
will  be  possible,  from  abnormal  distributions  of  atmos- 
pheric pressure,  to  predict  for  prolonged  periods  in 
advance  the  general  character  of  the  coming  season,  as 
warm  or  cold  and  wet  or  dry.  Unfortunately  for 
America,  it  seems  that,  owing  to  the  easterly  drift  of 
the  atmosphere,  the  ultimate  chances  of  such  predic- 
tions are  better  for  Europe  and  Asia  than  for  this 
continent. 

The  question  of  cyclical  variation  of  rainfall  coinci- 
dent with  sun-spots  has  been  very  fully  discussed  by 
Blanford,  so  far  as  India  is  concerned.  He  points  out 
the  peculiar  fascination  such  theories  exert  over  many 
minds,  and  he  emphasizes  the  necessity  for  rigorous 
scrutiny  of  all  such  cycles  by  a  general  array  of  facts. 
He  quotes  from  Russell  in  New  South  Wales  to  show 
that  cycles  for  periods  of  two,  three,  five,  six,  nine,  ten, 
eleven,  twelve,  thirteen,  seventeen,  nineteen,  thirty,  and 


AMERICAN   WEATHER.  271 

fifty-six  years  have  been  brought  forward  with  a  large 
amount  of  prima  facie  evidence. 

Blanford  examined  the  rainfall  of  all  India  for 
twenty-two  years,  and  in  arranging  the  rainfall  in 
the  biennial,  triennial,  etc.,  up  to  quinquennial  series, 
he  i  l  found  that  the  cyclical  series  could  always  be 
brought  out,  but  this  amplitude  proved  nothing  very 
different  from  the  probable  error  of  the  average." 
After  elaborately  discussing  the  rainfall  of  India  as  a 
whole  for  two  complete  sun-spot  cycles,  Mr.  Blanford 
says  :  "  It  may  therefore  be  confidently  concluded  that 
the  total  rainfall  of  India,  exclusive  of  that  of  Ceylon 
and  the  Burmese  peninsula,  and  (of  course)  of  the  seas 
around,  affords  no  evidence  whatever  of  an  eleven-year 
periodical  variation. ' ' 

An  examination  of  the  annual  mean  anomaly  of  the 
total  rainfall  of  India  for  twenty-one  years,  1864  to 
1885,  inclusive,  indicates  that  such  variations  are  acci- 
dental in  India  at  least. 

A  comparison  of  the  rainfall  of  separate  provinces 
shows  that  in  1871,  a  maximum  sun-spot  year,  the  pre- 
cipitation of  the  Konkan  was  14.6  inches  deficient, 
while  that  of  Malabar  was  2.4  inches  in  excess.  In  ten 
years  only  out  of  eighteen  did  the  four  rainfall  prov- 
inces of  India  have  the  same  sign  to  its  annual  deviation. 

A  similar  theory  as  to  the  prevalence  of  droughts  in 
the  years  of  minimum  sun-spots  and  of  heavy  rain  at 
the  sun-spot  maximum  has  found  many  supporters. 
Blanford  has  compared  the  record  of  sun-spots  and 
droughts,  and  makes  the  definite  statement  that  there 
is  no  "  dependence  of  the  one  class  of  phenomena  on 
the  other,"  since  the  record  shows  that  not  only  do 
droughts  occur  in  India  at  other  times  than  at  the  sun- 
spot  maximum,  but  even  "  sometimes  in  years  of  max- 
imum sun-spots." 


272  AMERICAN   WEATHER. 

In  connection  with  the  theory  that  the  temperature 
of  the  air  is  subject  to  variations  running  in  periods  of 
about  eleven  years,  in  inverse  order  to  the  number  of 
sun-spots,  Blanford  has  examined  the  temperature  of 
India  for  thirty-one  years,  from  1850  to  1880,  inclusive. 
He  says  :  "It  is  evident  that  there  is  no  indication 
whatever  of  an  eleven-year  period,  or  any  other,  in  the 
temperature  anomalies"  of  India. 

The  author  has  examined,  with  reference  to  the  in- 
fluence of  sun-spots  upon  precipitation,  the  following 
representative  stations :  San  Francisco,  Cal. ;  St.  Louis, 
Mo.  ;  Marietta,  O.  ;  Troy,  JN".  Y.,  and  Gardiner,  Me., 
from  1857  to  1887  ;  Cheyenne,  Wy.,  1870  to  1886  ;  and 
Omaha,  Neb.,  1870  to  1887. 

These  stations  were  selected,  as,  from  their  widely 
varying  longitude,  they  might  be  expected  to  be  rep- 
resentative stations,  covering  the  whole  area  of  the 
United  States.  There  was  only  one  year  in  which  the 
departures  of  these  stations  had  the  same  sign,  1864, 
when  there  was  a  deficiency  of  rainfall  at  five  stations. 
In  1866,  near  the  minimum  sun-spots,  there  was  an  ex- 
cess of  rainfall  at  four  stations  and  a  deficiency  at  one  ; 
in  1870,  the  year  of  the  maximum  sun-spots,  there  was 
a  deficiency  at  four  stations  and  an  excess  at  one  ;  in 
1874,  a  deficiency  at  five  and  an  excess  at  one  ;  in  1875 
an  excess  at  four  and  a  deficiency  at  three  ;  in  1876,  an 
excess  at  two  and  a  deficiency  at  five  ;  in  1878,  a  year 
of  maximum  sun-spots,  an  excess  at  five  and  a  deficiency 
at  two  ;  in  1880,  an  excess  at  two  and  a  deficiency  at 
five  ;  in  1884,  an  excess  at  five  and  a  deficiency  at  two. 

The  rainfall  data  at  these  stations  showed  no  connec- 
tion with  the  periodicity  of  sun-spots,  and  any  appar- 
ent connection  between  them  is,  in  the  opinion  of  the 
author,  entirely  accidental. 


AMERICAN  WEATHER. 


273 


TABLE  NO.  1.— CORRECTION  TO  BE  APPLIED  TO  BAROMETERS 
WITH  BRASS  SCALES,  TO  REDUCE  THE  OBSERVATION 
TO  32°  FAHRENHEIT. 


TEMPERA- 
TURE. 

INCHES. 

25.0 

27.0 

29.0 

29.5 

80.0 

30.5 

0 

20 

.019 

.021 

.022 

.023 

.023 

.023 

28 

.001 

.001 

.001 

.001 

.001 

.001 

29 

.001 

.001 

.001 

.001 

.001 

.001 

30 

.003 

.004 

.004 

.004 

.004 

.004 

35 

.015 

.016 

.017 

.017 

.018 

.018 

40 

.026 

.028 

.030 

.030 

.031 

.031 

45 

.037 

.040 

.043 

.044 

.044 

.045 

50 

.048 

.052 

.056 

.057 

.058 

.059 

52 

.053 

.057 

.061 

.062 

.063 

.064 

54 

.057 

.062 

.066 

.067 

.068 

.070 

56 

.061 

.066 

.071 

.073 

.074 

.075 

58 

.066 

.071 

.077 

.078 

.079 

.081 

60 

.070 

.076 

.082 

.083 

.085 

.086 

62 

.075 

.081 

.087 

.088 

.090 

.091 

64 

.079 

.086 

.092 

.094 

.095 

.097 

66 

.084 

.090 

.097 

.099 

.101 

.102 

68 

.088 

.095 

.102 

.104 

.106 

.108 

70 

.093 

.100 

.108 

.109 

.111 

.113 

72 

.097 

.105 

.113 

.115 

.117 

.119 

74 

.102 

.110 

.118 

.120 

.122 

.124 

76 

.106 

.114 

.123 

.125 

.127 

.129 

78 

.110 

.119 

.128 

.130 

.133 

.135 

80 

.115 

.124 

.133 

.136 

.138 

.140 

82 

.119 

.129 

.138 

.141 

.143 

.146 

84 

.124 

.134 

.144 

.146 

.149 

.151 

274 


AMERICAN  WEATHER. 


TABLE  NO.  2.— TABLE  FOR  REDUCING  OBSERVATIONS  OF  THE 
BAROMETER  TO  SEA-LEVEL,  CORRECTION  ADDITIVE. 


HEIGHT 
IN  FEET. 

TEMPERATURE  OP  EXTERNAL  AIR—  DEGREES  FAHRENHEIT. 

0- 

10° 

20" 

30° 

40° 

50° 

60° 

70° 

80' 

90» 

10 

.012 

.012 

.012 

.012 

.011 

.011 

.011 

.011 

.010 

.010 

20 

.025 

.024 

.023 

.023 

.023 

.022 

.022 

.021 

.021 

.020 

30 

.037 

.036 

.035 

.034 

.034 

.033 

.032 

.032 

.031 

.030 

40 

.049 

.048 

.047 

.046 

.045 

.044 

.043 

.142     .041 

.040 

50 

.061 

.060 

.059 

.058 

.056 

.055 

.054 

.053     .052 

.051 

60 

.074 

.072 

.070 

.069 

.068 

.066 

.065 

.063     .062 

.061 

70 

.086 

.084 

.082 

.081 

.078 

.077 

.076 

.074     .072 

.071 

80 

.098 

.096 

.094 

.092 

.090 

.088 

.086 

.084     .082 

.081 

90 

.111 

.108 

.105 

.104 

.101 

.099 

.097 

.095     .093 

.091 

100 

.123 

.120 

.117 

.115 

.112 

.110 

.108 

.105     .103 

.101 

150 

.185 

.180 

.176 

.172 

.168 

.165 

.162 

.158     .155 

.152 

200 

.246 

.240 

.234 

.229 

.224 

.220 

.215 

.210     .206 

.202 

250 

.307 

.300 

.293 

.286 

.280 

.275 

.269 

.263     .258 

.253 

300 

.368 

.359 

.351 

.343 

.3H6 

.329 

.322 

.315     .309 

.303 

350 

.429 

.419 

.409 

.400 

.392 

.384 

.376 

.368     .360 

.353 

400 

.489 

.478 

.467 

.457 

.447 

.438 

.429 

.420     .411 

.4(3 

450 

.550 

.537 

.525 

.513 

.503 

.492 

.482 

.472     .462 

.453 

500 

.610 

.596 

.583 

.570 

.558 

.546 

.535 

.524     .513 

.503 

550 

.670 

.655 

.640 

.626 

.613 

.600 

.587 

.575 

.564 

.553 

600 

.731 

.714 

.698 

.683 

.668 

.654 

.640 

.627 

.615 

.603 

650 

.791 

.773 

.755 

.739 

.723 

.708 

.692 

.679 

.666 

.653 

700 

.851 

.882 

.813 

.795 

.778 

.761 

.745 

.730 

.716 

.702 

750 

.911 

.891 

.870 

.851 

.833 

.815 

.797 

.782 

.767 

.752 

800 

.970 

.949 

.927 

.907 

.887 

.868 

.850 

.833 

.817 

.801 

850 

1.030 

1.007 

.984 

.962 

.942 

.922 

.902!    .885 

.867 

.851 

900 

1.089 

1.065 

1.041 

1.018 

.996 

.975 

.955     .936 

.917 

.9(10 

1,000 

1.208 

1.181 

1.154 

1.129 

1.105 

1.081 

1.059,  1.038 

1.017 

.998 

1,100 

1.326 

1.296 

1.267 

1.239 

1.213 

1.187 

1.163;  1-140 

1.117 

1.096 

1,200 

1.444 

1.411 

1.379 

1.349 

1.321 

1.293 

1.266]  1.241 

1.217 

1.193 

1,300 

1.561 

1.525 

1.491 

1.459 

1.428 

1.398 

1.369 

1.342 

1.316 

1.21)0 

1,400 

1.678 

1.639 

1.603 

1.568 

1.535 

1.503 

1.472 

1.443 

1.415 

1.387 

1,500 

1.794 

1.753 

1.714 

1.677 

1.641 

1.607 

1.574 

1.543 

1.513 

1.484 

AMERICAN   WEATHER. 


275 


TABLE  NO.  3.— APPROXIMATE  CORRECTIONS  TO  REDUCE 
BAROMETER  READINGS  AT  8  A.M.  AND  8  P.M.,  75-TH 
MERIDIAN  OR  EASTERN  TIME  TO  THE  DAILY  MEAN. 


8  A.M. 

8  P.M. 

-  .02  in 
-.02 
-  .02 
-  .02 
-  .02 
-  .02 
-.02 
-  .01 
-  .03 
-  .04 
-  .03 
-  .01 
-  .02 

+  .01 

+  .01 
-.03    • 

ch 

< 

i 
i 
< 

( 
i 
< 
t 

< 
( 

i 
t 

-  .01  in 
-.02 
-.00 

h.oi 

-.02 
-.01 
-.03 
-.01 
-.03 
\-  03 

ch 
f 

Bismarck    Dak  

Buffalo   N.  Y  

Chicago   111  

Denver   Col  

Key  West   Fla        

Montgomery  Ala 

-102 
-.03 
-.03 
-.02 
-.02 
-.01 

Portland    Ore              

Salt  Lake  City  Utah  

San  Diego  Cal  

San  Francisco,  Cal  

Washington  D  C  

TABLE  NO.  4.— APPROXIMATE  CORRECTIONS  FOR  REDUC- 
ING THE  MEAN  OF  THE  MAXIMUM  AND  MINIMUM 
TEMPERATURES  TO  THE  TRUE  MEAN  OF  THE  DAY. 


January. 

July. 

San  Diego  Cal  

—  0.7° 

-  0.3° 

—  0.4° 

-  0.1° 

Washington  DC        

—  0.9° 

—  0.8° 

Denver    Col      

-  o.r 

-  0.8° 

-  0.0° 

-0.2' 

Frankfort  Arsenal  Pa  *          ... 

—  0.8° 

-  0.1° 

*  From  Guyot's  Tables. 


276 


AMERICAN  WEATHER. 


TABLE  NO.  5.— SHOWING  VAPOR  TENSIONS  AND  ABSOLUTE 
HUMIDITIES  FOR  DEW-POINTS  OF  VARIOUS  TEMPER- 
ATURES. 


1 

H  n 
fig 

» 

Absolute  Hu- 
midity, Grains  of 
Water  to  each 
Cubic  Foot. 

il 

is 

Vapor 
Tension. 

Absolute  Hu- 
midity, Grains  of 
Water  to  each 
Cubic  Foot. 

-40° 

0.01 

.08 

66° 

0.45 

5.02 

-30 

.01 

.13 

58 

.48 

5.37 

-20 

.02 

.22 

60 

.52 

5.75 

-10 

.03 

.36 

62 

.56 

6.14 

0 

.04 

.56 

64 

.60 

6.56 

10 

.07 

.87 

66 

.64 

7.01 

20 

.11 

1.32 

68 

.68 

7.48 

30 

.17 

1.96 

70 

.73 

7.98 

35 

.20 

2.37 

72 

.78 

8.51 

40 

.25 

2.85 

74 

.84 

9.07 

45 

.30 

3.42 

76 

.90 

9.66 

50 

.36 

4.08 

78 

.96 

10.28 

52 

.39 

4.37 

80 

1.02 

10.94 

54 

.42 

4.69 

90 

1.41 

14.79 

*  For  considerable  elevations  about  .01   should  be  added  for  each 
thousand  feet. 


TABLE  NO.   6.— MAGNETIC  VARIATIONS  IN  1888. 
Variation  east  is  when  the  compass  points  to  the  east  of  the  true  north. 


VARIATION  EAST. 

De- 
grees. 

Min- 
utes. 

VABIATION  WEST. 

De- 
grees. 

Min- 
utes. 

15 

35 

Boston,  Mass  

11 

55 

Brownsville  Tex.  .  .  . 

7 

35 

Buffalo  N.Y  

5 

10 

Chicago   111  

4 

00 

Charleston,  S.  C  

o 

00 

Denver   Col 

14 

15 

Cleveland    O  

1 

35 

El  Paso  Tex     

12 

00 

Detroit   Mich  

o 

30 

Helena,  Mont    

19 

55 

Eastport,  Me  

18 

55 

Jacksonville,  Fla.  .  .  . 
New  Orleans  La     . 

2 
6 

00 
00 

Lynch  bur^,  Va  
New  York  City  

1 

8 

25 
20 

Olympia   Wash   Ty  . 

21 

40 

Northfield   Vt  

12 

50 

Omaha   Neb  

10 

10 

Pittsburg,  Pa  

3 

00 

San  Diego   Cal  

13 

35 

Washington,  D.  C... 

4 

10 

San  Francisco,  Cal.  .  . 

16 

35 

Wilmington,  N.  C.  .  . 

0 

50 

AMERICAN   WEATHER. 


277 


TABLE  NO.  8.— HEAVIEST  MONTHLY  RAINFALLS  EVER 
RECORDED  IN  THE  VARIOUS  STATES. 


STATE. 

Station. 

Month. 

Year. 

Eainfall 
in  Inches. 

Opelika  .        .   . 

July  .  . 

1887 

20  13 

Arizona.               • 

August 

1SKO 

14.  45 

Lead  Hill 

October 

1883 

18  11 

California  

Upper  Matole 

January 

1888 

41  60 

Trinidad 

June.  .  .  . 

1878 

12  83 

Connecticut  

Canton 

May  

1868 

18  00 

Dakota  

Webster 

July 

1884 

14  65 

Delaware              .  . 

Fort  Delaware 

Septemb6r 

lSf»H 

19  85 

District  of  Columbia 
Florida  

Washington  
Ft  Barrancas 

July  
August 

1886 
1878 

10.63 
30  73 

Raburn  Grap 

October 

1877 

19  40 

Idaho       

Lewiston 

June 

1884- 

5  63 

Illinois      

Cairo 

January 

187fi 

15  05 

[ndianapolis 

July 

1875 

13  12 

Fort  Gibson 

July 

1875 

11  89 

Iowa           

"^ockford 

T  y  

June 

Iftft*; 

18  70 

Kansas  

Elk  Falls 

April 

1885 

19  00 

Louisville 

July 

1875 

16  46 

Alexandria        . 

June 

1886 

3691 

Maine  

Dastport 

May 

1881 

13  22 

Maryland  

St  John's  Church 

May 

1881 

12  30 

Amherst 

July  

1874 

12  61 

Michigan  

S^orthport  

May  

1884 

19.85 

Sylvan  Park 

July. 

1872 

21  86 

Jackson 

April  .  . 

1874 

2380 

Missouri  

St  Louis 

******  

June 

1848 

17  07 

Fort  Ellis 

June 

1885 

12  26 

Nebraska  . 

Table  Rock 

Tune 

1883 

17  07 

Nevada  

Fort  McDermit 

April 

1883 

13  00 

New  Hampshire  

Mt  Washington 

Julv 

1884 

2390 

Newark  .    .  . 

August  . 

1843 

22  50 

New  Mexico  

^ort  Union  

August  

1886 

8.04 

Trov 

October 

1869 

1380 

North  Carolina  

Asheville  .   . 

Au  trust  . 

1887 

2865 

Ohio      

Carthagenai 

une 

1877 

17  33 

Oregon    

Pennsylvania  

Astoria  

Wellsboro  .  .  . 

anuary  
August.. 

1880 
1885 

29.80 
15.25 

Rhode  Island.  .  . 

•lock  Island 

une 

1881 

1293 

South  Carolina  

Charleston           ... 

Au  2rust 

1885 

19.18 

Tennessee  

White  

July  .  . 

1883 

28.11 

Texas  „. 

irownsville 

September  .  . 

1886 

30.57 

Utah  

Mt  Carmel 

1877 

10.00 

Vermont  

Draftsburg 

October  .... 

1869 

10.72 

Virginia  

Dape  Henry  

A.ugust  

1887 

16.82 

Washington  Terr.  .  .  . 

December  .  .  . 

1886 

30.70 

West  Virginia  

Helvetia     

A.U  crust  .  . 

1882 

12.60 

Wisconsin  

feillsville 

eptember 

1881 

14.01 

Wyoming  

Hat  Creek  

kpril  

1879 

6.93 

278 


AMERICAN   WEATHER. 


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AMERICAN   WEATHER. 


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INDEX. 


Absolute  zero  of  temperature,  129. 
Actinometers,  35. 
Actinometry,  36,  41. 
Air,  Composition  of,  2.    Selective 

absorption  of,  36.    Temperature 

of,  18. 

Air-thermometer,  Invention  of,  1. 
Anemometers,  54,  57.    Errors  of, 

188.    Register,  55. 
Anthelia  or  glories,  261. 
Anti-cyclones,  202-210.    Paths  of, 

212-222. 
Atmometer,  46. 
Atmosphere,   Absorption  of  heat 

by,  41.    Height  of,  2.    Physical 

conditions  of,  3. 
Atmospheric  electricity,  257. 
Atmospheric  pressure,  5.    Defined, 

5.    Distribution  of,  82-84,  92- 

93  ;  in  the  United  States,  89-92. 

How  measured,  5.   Fluctuations 

of,  84,  85,  88.    Types  of,  84-87. 

Variations  of,  93,  94.     When  it 

is  high  and  when  it  is  low,  83, 

84.    Unusually  high  and  low,  98. 
Aurora  borealis,  262. 

Balloon  ascent  of  Glashier,  2. 

Barometer,  Aneroid,  12.  At  Arc- 
tic stations,  95.  Care  of,  12. 
Corrections  of,  9.  Daily  ampli- 
tude, 96.  Described,  5.  Draper's, 
15.  Fortin's,  5.  Gibbon's,  15. 
Hough's,  15.  How  to  read  it, 


18.  Invention  of,  1.  Metallic 
(Bourdon's),  13.  Oscillation, 
Cause  of,  94.  Principle  of,  5. 
Range  of,  97,  99.  Richard's, 
16.  Self-recording,  15.  Siphon, 
8.  Standard,  7.  Unusually 
high  and  low,  98. 

Barometric  gradient,  179.  Obser- 
vations, Reduction  of,  90. 

Barral,  J.  A.,  mock  suns,  262. 

Baudin's  minimum  thermometer, 
25. 

Beaufort  wind  velocity  scale,  54. 

Bixio,  mock  suns,  262. 

Blanford,  H.  F.,  cyclones  in  In- 
dia, 196.  Rainfall,  135,  153, 
155.  Rainfall  and  sunspots, 
270,  271.  Temperature  and 
sunspots,  272. 

Blizzards,  167,  205,  211,  222.  Re- 
markable, 222-227. 

"  Borrowing  days,"  117. 

Bourdon's  metallic  barometer,  13. 

Bravais,  A.,  pseudohelion  or  mock 
sun,  262. 

Buist,  G.,  hailstones,  78.  Hail- 
storms in  India,  236. 

Bura  winds,  167. 

Buster  winds,  167. 

Buys  Ballot's  law  of  winds,  195, 202. 

Caloric  defined,  36. 
Campbell- Stokes  sunshine  record- 
er, 40. 


282 


AMERICAN   WEATHER. 


Carpenter,  W.  B.,  mild  climate  of 
northwest  Europe,  104. 

Centigrade  scale,  21. 

Chinook  winds,  166. 

Cirro-cumulus  clouds,  63. 

Cirro-stratus  clouds,  63. 

Cirrus  clouds,  63. 

Climate,  Continental,  120.  Marine, 
120. 

Cloud-bursts,  148-150. 

Cloudiness,  Average,  64-66.  Fluc- 
tuations of,  65,  67,  68.  How 
recorded,  64. 

Clouds,  Classification  of,  63.  Ele- 
vation of,  64.  Forms  of,  63. 
Upper  and  lower,  64. 

Cold  waves,  118.  Defined,  211. 
Remarkable,  216-222. 

Coronas,  259. 

Corrections  applied  to  barometer 
readings,  9.  For  altitude,  11. 
For  capillary  action,  10.  For 
temperature,  10. 

Cumulo-stratus  clouds,  63. 

Cumulus  clouds,  63. 

Cyclones,  193.  Remarkable,  193- 
201. 

Cyclonic  and  anti-cyclonic  storms, 
180,  191.  Motion  of,  181.  Shape 
of,  181,  191.  Tracks  of,  182. 

"  Degrees  of  frost,"  22. 

Dew,  68,  69,  156.    Amount  of,  69. 

Dove,  H.,  the  march  of  weather 
phenomena,  206. 

Draper,  D.,  rainfall  of  New  York 
City,  155. 

Draper  self-recording  thermom- 
eter, 27,  28. 

Droughts,  246.  Disastrous,  248- 
250.  Connection  with  sunspots, 
270,  271. 

Dry  fogs,  245. 

Dust  storms,  244. 


Earth  temperatures,  256. 

Eccard  rain-gauge,  75,  76.  Trans- 
mitting barometer,  15.  Wind 
vane,  54. 

Ekholm  and  Hagstrom,  height  of 
clouds,  64. 

Electricity,  Atmospheric,  257. 

Eliot,  J.,  hailstones  in  India,  237 

Ellis,  Henry,  blizzards,  222. 

Errors,  Thermometer,  24.  Sources 
of,  25. 

Evaporation,  43-46.  Annual 
amount  of,  48.  At  Fort  Con- 
ger, 48. 

Evaporometers,  46,  47. 

Fahrenheit  scale,  21. 

Ferrel,   W.,  tornadoes,  230,  233. 

Axis  of  storm,  231. 
Finley,   Lieut.  J.  P.,    tornadoes, 

229,  231,  233. 
Flammarion,  C.,  paranthelion   or 

mock  sun,  262. 
Foehn  winds,  166. 
Fog,  60,  61.  In  Arctic  regions, 

61.     On  North  Pacific,  61.     On 

Atlantic  coast,  62.      Relation  to 

storms,  62. 
Fog,  Dry,  245.    Remarkable,  244. 

Bows,  259. 
Fortin's  barometer,  5. 
Franklin,  B.,  electrical  phenomena 

of    storms,     242.       Northwest 

storms,  205. 
Frost,  Degrees  of,  22. 
Frosts  in  the  United  States,  269. 

How  to  foretell,  269. 

Garriott,  E.  B.,  fogs  on  the  Atlan- 
tic coast,  62. 

Gibbon,  Lieut.,  anemometer  reg- 
ister, 58. 

Gibbon's  anemometer,  54.  Self- 
recording  barometer,  15. 


AMERICAN   WEATHER. 


283 


Glashier's  balloon  ascent,  2. 
Glories  or  anthelia,  261. 
Gregale  winds,  167. 
Gulf  Stream,  Effect  of,  104. 

Hagstrom  and  Ekholm,  height  of 

clouds,  64. 
Hail,   77,  78.    Formation  of,  80, 

81.     Structure  of,  78,  79.     Typ- 
ical forms  of,  79. 
Hailstorms,  235.    Destructive,  235- 

241. 
Halos,  259,  260.     As  indicators  of 

rain,  261. 

Hann,  J.,  Foehn  winds,  166. 
Harkness  hair  hygrometer,  49. 
Harmattan  winds,  166. 
Haze,  245. 

Hazen,  H.  A.,  thunderstorms,  235. 
Heated  terms,  246.     Cases  of,  250- 

254.     Causes  of,  247,  250,  253. 

Fatal  effects  of,  254.  Frequency 

of,  253. 
Hellmann,  G.,  lightning  strokes, 

243. 

Hoar-frost,  70,  72. 
Hough's  self-recording  barometer, 

15. 
Howard,   classification  of  clouds, 

63. 

Humidity  and  tornadoes,  229. 
Humidity,  45.    Relative,  51.    Ab- 
solute, 49. 

Hurricanes,  193-201. 
Hygrometer,  48.    Hair,  48.    Kop- 

pe's,  49. 
Hygroscopes,  48. 

Ice,  Formation  of,  by  radiation  and 

evaporation,  44. 
Isobars,  182. 
Isotherms,  101, 103,  109,  112,  128. 

"  January  thaw,"  117. 


Khamsin  winds,  166. 
Koppe's  hair  hygrometer,  49. 

Langley,  Actinometry,  38,  40,  41. 
Laughlin,   Prof.   J.   A.,   halos  as 

indicators  of  rain,  261. 
Leveche  winds,  166. 
Lightning,  Globular,  242.     Return 

shock,  242.     Safety  from,  243. 
Lightning  rods,  243.     Strokes  and 

character  of  soil,  243. 
Loomis,  E.,  to  obtain  true  mean 

temperatures,  33. 
Lunar  halos,  259.   At  Fort  Conger, 

260.  Rainbows,  259. 

Macintosh,  J.  S.,  hailstorms  in 
India,  236,  237. 

Marvin,  C.  F.,  sunshine-recorder, 
40.  Rain-gauge,  75. 

Meldrum,  C.,  thunderstorm  con- 
ditions. 241. 

Mirage,  262. 

Mistral  winds,  167- 

Mists,  61. 

Mock  moons  at  Fort  Conger,  260, 

261.  Suns,  260,  261 ;   in  Grin- 
nell  Land,  261. 

Mohn,  H.,  high  barometer,  83. 
Monsoons,  163. 
Moritz,  A.,  hailstones,  80. 
Mountains,     Influence      of,      on 

weather,  etc.,  104. 
Murray,  John,  rainfall,  134. 

Negretti  and    Zambra  maximum 

thermometers,  26. 
Nimbus  clouds,  63. 
Nipher,  F.  E.,  dust  storms,  244. 
Northeast  storms,  205-210. 
Northers,  167,  205-210. 
Ocean  currents,  Effect  of,  104. 
Optical  phenomena,  257. 
Ozone,  257. 


234 


AMERICAN   WEATHER. 


Pampero  winds,  167. 

Paranthelion  or  mock  sun,  262. 

Paraselense,  261. 

Parhelia  or  mock  suns,  261. 

Phillips's  maximum  thermometer, 
26. 

Piche  evaporometer,  47. 

Precipitation,  60.     See  Rainfall. 

Prediction  of  weather,  264-270. 
Difficulties  of,  265,  266.  Gen- 
eral rules  for,  267.  Long  range, 
268,  270.  Mental  qualities  nec- 
essary for,  267. 

Pressure,  Atmospheric,  5.  Daily 
means  of,  17.  How  measured, 
5.  See  also  Anti-cyclones  and 
Atmospheric  pressure. 

Psychrometer,  Mounted,  30. 
Whirled,  29. 

Purga  winds,  167. 

Radiation  defined,  35.  Nocturnal, 
42,  204.  Solar,  40.  Terrestrial, 
35,  41-43. 

Rainbows,  259.    Lunar,  259. 

Rain,  60.  Colored,  73,  74.  Dis- 
tribution of,  134-136, 140.  From 
cloudless  sky,  72.  Regions 
without,  138.  Wet  months  and 
dry  months,  139. 

Rainfall,  70,  71.  Average  amount, 
134,  135,  150.  Excessive,  138, 
144-146,  149.  Extraordinary 
showers  of,  147.  Fluctuations 
of,  141,  156.  Frequency  of,  150. 
Heat  from,  111.  In  India,  138, 
146.  Influence  of  forests  on, 
155,  157.  Least  amount,  134, 
138.  New  York,  156.  Pacific 
coast,  136.  Variability,  153, 
154. 

Rainfall  curves,  Average,  143. 
Types  of,  140-142.  Variations 
of,  142. 


Rainfall,  droughts,  and  sunspots, 

270. 
Rain-gauge,  55,  74.    Elevation  of, 

76.     Signal  Service,  74,  75. 
Rainless  months,   144.     Regions, 

138. 
Rainy  days,  Average  number,  152. 

Distribution  of,  151.     Probabil- 
ity of,  151. 

Reaumer  thermometer  scale,  21. 
Richard's    self-recording  aneroid, 

16.  Self-recording  thermometer, 

26. 

Riegler,  W.,  evaporation,  47. 
Robinson's  anemometer,  57. 
Russell,  H.  C.,  rainfall  cycles,  270. 
Russell,  T.,  rain  from  clear  skies, 

72. 
Rutherford  thermometers,  23,  26. 

Errors  of  25. 

Sdrocco  winds,  166. 

Scott,  R.,  halos,  260.  Sunset 
colors,  259. 

Sea  temperatures,  255. 

Self-recording  instruments,  13,  15, 
16,  22-28,  40,  74. 

Siphon  barometer,  8. 

Six's  thermometers,  23. 

Snow,  60.  Colored,  74.  Distribu- 
tion of,  158.  From  cloudless 
sky,  72.  How  measured,  77. 
In  the  United  States,  159.  Re- 
markable snowfalls,  160,  161. 
Structure  of,  77. 

Snow,  F.  H.,  heated  terms,  251. 

Snow-gauge,  77. 

Solar  constant  defined,  36,  41. 
Radiation,  40. 

Solar  halos,  259,  260.  In  Arctic 
regions,  259,  260.  Remarkable, 
261. 

Storms,  178.  Avoidable  quad- 
rants, 190.  Course  of,  183,  185, 


AMERICAN   WEATHER. 


285 


188,  189.  Dangerous  quadrants, 
190.  Frequency  of,  183,  184. 
Movement  of,  in  relation  to  up- 
per currents,  186,  187,  190. 
Northers,  205-210.  Velocity  of, 
184,  185,  191.  West  Indies,  189. 
See  also  Winds. 

Storm  axis,  231. 

Stratus  clouds,  63. 

Sunset  colors,  258,  259. 

Sunshine-recorder,  40. 

Sunspots  and  precipitation,  270. 
In  India,  271,  272.  In  United 
States,  272. 

Temperature  of  air,  18.  Absolute 
range,  121.  Absolute  zero,  129. 
Annual  fluctuations,  107,  125, 
126.  Black  and  bright  bulb,  39. 
Cold  days  of  May,  117,  118. 
Coldest  and  warmest  months, 
115,  116.  Daily  fluctuations, 
113,  124.  Daily  means,  33.  Dis- 
tribution of,  100.  Diurnal 
march,  112.  Extremes  of,  121, 
123,  128,  129.  Great  differences, 
112.  High,  38,  109,  110.  In- 
terruptions  of,  and  low  area 
storms,  118.  Low,  109,  110, 
130-132.  March  of,  107,  108, 
112.  Maximum  and  minimum, 
112,  113,  116,  127.  Means,  101, 
106, 114,  115.  Normal  for  May, 
117.  Pacific  coast,  110.  Of  sea, 
102,  103.  Ranges  of,  120,  121, 
123,  125,  126.  Topography, 
Effect  of,  on,  211.  Variability, 
132. 

Temperatures,  High,  252,  253.  Of 
earth,  256.  Of  sea,  255.  Sun- 
spots,  272.  Tornadoes,  229. 

Thermometers,  1,  18.  Bright  and 
black  bulb,  36,  39.  Changes  of, 
20.  Draper,  27,  28.  Errors, 


19,  24,  25.  Exposure,  28.  In- 
vention, 1,  23.  How  to  correct, 
24.  Maximum,  26.  Mercurial, 
19.  Minimum,  23.  Minimum 
d  marteau,  25.  Mounted,  30, 
32.  Negretti  and  Zambra,  26. 
Phillips,  26.  Richard's,  26,  27. 
Rutherford's,  23.  Scales,  21. 
Self-recording,  22.  Shelter,  29. 
Six's,  23.  Spirit,  19,  23.  Test- 
ing of,  21.  Ventilation,  31. 
Wet  and  dry  bulb,  30,  51. 
Whirled,  29. 

Thermometric  gradient,  179. 

Thunderstorms,  235,  241.  Elec- 
trical phenomena  of,  242.  Fre- 
quency of,  241. 

Tornadoes,  228.  Destructive,  231, 
232,  234.  Distribution,  233. 
Favorable  conditions,  230. 
Frequency,  231.  Humidity, 
229.  Ferrel,  230.  Finley,  229. 
Path  of,  233.  Temperature, 
229. 

Trades  and  anti-trades,  163. 

Tramontanes  winds,  167. 

Typhoons,  189. 

Upton,  W.,  blizzard  of  March  11- 
14,  1888,  225. 

Ventilation,  Thermometer,  31. 
Vernier,  8. 

Water-spouts,  148,  149,  150,  234. 

Weather-glass,  12. 

Weather  prediction,  264-270.    In 

United  States  Weather  Bureau, 

264.     See  also  Prediction. 
Weber,  Prof.   H.,  golden   snow, 

74. 

Wells's  theory  of  dew,  68. 
Wet    and    dry    months    defined, 

139. 
Whirlwinds,  228. 


286 


AMERICAN   WEATHER. 


Wind— Average  velocity,  169, 171, 
173,  174.  Classification,  163. 
Fluctuations,  170.  High,  175. 
How  measured,  53.  Light,  175. 
At  Mt.  Washington,  186,  188. 
Relation  of,  to  course  of  storms, 
164.  Remarkable  systems  of, 
172.  Remarkable  storms,  176, 
177.  At  Washington,  D.  C., 
168.  Vane,  54,  55.  Velocity 
scale,  54. 

Wind-gauge,  56. 

Winds— Blizzard,  Bura,  Buster, 
167.  Chinook,  Foehn,  166. 


Gregale,  167.  Harmattan, 
Khamsin,  Leveche,  166.  Mis- 
tral, 167.  Monsoon,  163. 
Northers,  Pampero,  Purga,  167. 
Scirocco,  166.  Trades,  163. 
Tramontana,  167.  Prevailing, 
164,  165.  Of  the  United  States, 
163. 

Woodruff,  Lieut.  T.  M.,  temper- 
ature changes,  215. 

Zambra  and   Negretti   thermom- 
eters, 26. 


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